Aliens: Fireteam Elite Hidden Cache Locations

Physical description
Hidden caches are flat orange crates with two bright yellow lights on each bottom corner. They are the same standard size as the grey consumable crates that are located at swarm defense points where you find ammo crates and med kits together.
A black and white crate symbol appears above them, this can be viewed at a considerable distance as long as the crate is in line of sight.What do they contain?
They each generally contain three different items, generally a weapon attachment(unless you have them all), a cosmetic, an emote, consumables and challenge cards. Rarely you can get a 4th drop from a cache which include brand new perks e.g. “Creative Pain Point Solutions” for Tech. They are the fastest way to get new attachments besides completing missions with “Form An Attachment” challenge card and the selection you can buy directly from the shop. You will always get a unique item when possible, not something you already own, with the exception being consumables.

Mechanics
One cache will spawn in every level in a random location. The locations it can spawn in are fixed, so knowing where to look and then not looking after you find one will speed up game play considerably. There are approximately 8 different spawn locations per level (to be confirmed).
Opening 50 hidden caches will award you with an achievement called Keen Eye.
You will keep the loot even if you die or abandon the mission, so they have potential to reduce grind. Difficulty does not seem to increase the loot in cache the same way it affects end of mission rewards, although its random.

How to find them?
The ones I’ve found so far can typically be found by looking behind you as you progress towards the marker. There are a few exceptions where they are located off towards the side. They are generally visible without going off the path if you happen to look in the right direction, again there are some exceptions and these might just be the easiest ones to locate. If you find a new one, please write in the comments so I can add it to the list and narrow down possibilities.

Sometimes, hidden caches are very well hidden, popping up behind random tents or in caves on dead-end paths. They can spawn near Intel sometimes.

All caches will be listed in the order you can find them where possible. Requires knowing all of the locations for a level and an accurate description of where to find them.

Priority One: Ingress
1.1.1 Opposite the first door you are told to cut through, behind you, behind some boxes.
1.1.2 “Unlock Exits”, 1st working Joes area, second(far) back left room, in opposite corner.
1.1.3 “Prepare for Battle”, down far stairs, near facehugger, head towards “giant Dalek head”.
1.1.4 3-way ambush (after drone ambush), inside working Joes area, on the left.
1.1.5 Ammo box ambush (prowlers, bursters), downstairs, far left corner past Intel.
1.1.6 Ammo box ambush (prowlers, bursters), upstairs, turn around at exit doorway before you leave for the last time (2nd time if you get the random side mission). Behind some boxes.
1.1.7 Huge coolant room with internal leaks and safety rails. Turn left as you enter(chance of prowler).
1.1.8 After coolant room, past bursters and %prowler. On the left, enemies may spawn from there. Last chance to grab it as the next door seals you into the final defense area.
Final defense notes: Its possible to wipe out the aliens with at least 20 seconds to spare, then nothing will spawn for 20 seconds. The final wave only spawns when the elevator timer hits 0.

Priority One: Rescue
1.2.1 “Override Door Lockdown”, defense area, up the stairs on the left as you enter this area. In a corner behind consoles that will be in front of you as you reach the top of those stairs.
1.2.2 “Override Door Lockdown”, defense area, up the stairs on the right as you enter this area. Look left and it will be up against wall in the opposite corner.
1.2.3 “Locate Valve”, take a left twice, the tiny storage room on the left and the first valve room to check. It will be on the right wall (%prowler).
1.2.4 “after Unlock Inner Door” After 1st Monica encounter, from ammo box, go down, take first right in crate maze and its on the left.
1.2.5 Same area, from ammo box, go down and straight ahead, in front of a spawn vent, behind large trapezoidal dumpster crate.
1.2.6 Same area, when about to leave(Bashi Tower Centcomp A Deck 41), instead of going into red lit area, turn left to stay in the same area, then turn right and its next to a closed door.
1.2.7 confirmed a 7th spawn exists
1.2.8
Bonus: Notes on Monica
After the Prowler on the right spawns, she will run down the middle from where you came from, then dive into the hole on her left. She will then come out of the opposite hole on the right. With known pathing she can probably be cheesed with mines.

Priority One: Extract
1.3.1 As you exit waste disposal/sewers, turn right instead of left. Across this bridge (opposite waypoint marker), under 2m crate with an X and next to blue barrel.
1.3.2 Next area(inside). Take a right instead of the waypoint door 13m ahead, then another right into dead-end.
1.3.3 “Prepare for Battle”, go down the stairs on the right and check around the corner, before the red meters, next to the two piles of pipes.
1.3.4 After you check synths for a door code and bypass the door. Instead of going left and down into the pool, go to the end and look inside the doorway to the right and it will be filling the doorway.
1.3.5 Beltway area. Directly below the beltway, beltway-side/red meters in the middle.
~2nd Intel.
1.3.6 “Investigate Hangar Delta”, take a 180 left before the loading arm and go up the stairs behind you up to the tower control room door(closed).
1.3.7 Next area, long corridor with red meters on the right. At 47m to waypoint door, take the dim side corridor on the right, and then a left, and its in the small vented area in the middle left.
1.3.8

Giants in the Earth: Insertion
2.1.1 After church-like area with large pipes upperleft and right, take the side corridor on the left. Before “bug swarm” battle and 2nd Intel. Also a strong fallback position.
2.1.2
2.1.3
2.1.4
2.1.5
2.1.6
2.1.7
2.1.8

Giants in the Earth: Contact
2.2.1 “Prepare for Battle”, behind the first wall. (On the right if you turn around, on left as you enter)
2.2.2
2.2.3
2.2.4
2.2.5
2.2.6
2.2.7
2.2.8

Giants in the Earth: Evacuate
2.3.1
2.3.2
2.3.3
2.3.4
2.3.5
2.3.6
2.3.7
2.3.8

The Gift of Fire: Recon
3.1.1 In the first large area, take a left and its on the right next to a blue cylinder light.
3.1.2
3.1.3
3.1.4
3.1.5
3.1.6
3.1.7
3.1.8

The Gift of Fire: Advance
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
3.2.6
3.2.7
3.2.8

The Gift of Fire: Boarding
3.3.1
3.3.2
3.3.3
3.3.4
3.3.5
3.3.6
3.3.7
3.3.8

The Only Way To Be Sure: Breach
4.1.1
4.1.2
4.1.3
4.1.4
4.1.5
4.1.6
4.1.7
4.1.8

The Only Way To Be Sure: Search
4.2.1
4.2.2
4.2.3
4.2.4
4.2.5
4.2.6
4.2.7
4.2.8

The Only Way To Be Sure: Regicide
4.3.1 In a room shaped like a grid, instead of following marker to right, go straight ahead.
4.3.2
4.3.3
4.3.4
4.3.5
4.3.6
4.3.7
4.3.8

1. Change from Windowed Borderless to Fullscreen
or
2. Add “-LockMouse” to launch options (untested, works in another game)

The game produces full crash logs and stores them in the Appdata folder each time the game crashes. These folders can be over 8gb each. See folder: Main Drive/Users/(profile)/Appdata/Local/Endeavor/Saved/Crashes

DEVELOPER – The game crashes whenever the game is ‘deselected’ or alt-tabbed while loading the Endeavor or into a mission and this produces one of these logs, having the logs is one thing but the fact it is producing the whole log and storing it could completely crash and bugger up peoples computers (from my knowledge), this should be rectified and compressed/only key files saved.

Circumstances that can cause crash while playing in fullscreen and whenever the game is on a loading screen include the mouse being no longer ‘bound’ to the window, causing a crash if the game thinks you have clicked away from the screen or if one actually presses “alt-tab”. The games loading circle will freeze, the game itself will freeze and slow down the system including how long it takes to open Task Manager. A UE4 crash window will appear and a crash report will be generated on C/main drive in above location. The longer you have been playing the larger the crash log but they can start off large or after just a single mission if you crash going back to the Endeavour.

Armature: Quick Charge Armature
+25% Reload Speed
+15% Fire Rate, +30% Stability on Hit for 5 seconds (assuming this part isn’t bugged)Armature: Deep Railed Armature
+30% Reload Speed
+20% Max Ammo

Barrel: Miller Twist Rifling
+20% Stability
+20% Handling
20% chance on Hit: Enemies are Slowed by 50% for 10 seconds
Useful on any weapon with a high fire rate and/or area of effect, noticeably the Smart Gun. Applies a visible debuff to the enemy.

Magazine:
Specials effects may be bugged. Needs further testing.

Muzzle:
Specials effects may be bugged. Needs further testing.

Optics:
Specials effects may be bugged. Needs further testing.

Go debrief with the crew in the Endeavour.

This question has been showing up in one form or another on every page in Steam and its always because you need to talk to the crew. So I put the answer here.