My AMS Lite didn’t recognise filament until I realised I put the filament in a different slot as the spool is. The sequence is 1-4 on the back and 2-3 on the front. After correcting the slots everything is smooth now. Maybe a stupid mistake I made, but it can happen to anyone I think 
Thanks - that worked, and the hypothesis sounds correct.
I have no idea what steps you are taking. Please do not use shortcuts some people like me is beginner,
Step 1: Resync filaments from AMS: (FROM WHERE)
Step 2: Right-click (or your system equivalent of right-click) on your model (which should be showing on your plate in Bambu Studio).
ANY IMAGE ? not sure where to right click
Step 3: This should bring up the context menu. Then select Change Filament.
stuck on above
Step 4: Wait for your print to finish 
no its does not help
Seems like I have a similar trouble. There is one selection of filaments actually in AMS, and there is a selection in “Device” tab. The one in “Device” has wrong filament in Slot 1 - and I can not edit it. Any idea how to fix this?
TL;DR: Screwed up in color painter, object still had miniscule layer of external filament, use the “Bottom” pop-up to ensure precise layer-filament selection.
Had the same issue, ended up being my own carelessness in the color painter. Mistakenly selected the TPU I had set in the manual/external filament slot when painting by layer; realized my mistake in the moment and tried to eyeball the layer line when I replaced it with the correct PLA filament in the AMS. Missed it by .02 mm, which was less than my layer height of .08 mm, but slicer didn’t seem to care about that; .02mm of external filament on the object was enough to make AMS throw a fit. Went through and fixed it using exact measurements for each color via the “Bottom” pop-up, which in turn cleared out the tiny bit of residual TPU painting and everything worked fine.
How is this 1 year later STILL A PROBLEM!
PLA in slots 1 - 3 and PETG in slot 4, cannot print.
All you get is “only the AMS slots loaded with the same material type can be selected”.
Obviously I want to keep the PETG in the AMS or I have to keep drying it out.
Setting the color on the object is a workaround but this bug should have been fixed long ago.
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I was having the same problem. Believe it or not, it was the PRINTER SETTING. I had physically changed nozzles and updated that at the printer. I also made sure it was reflecting the proper nozzle change over in Bambu Studio. My printer setting said Bambu Lab A1 Mini but when I hit the pull-down there, there were two additional selections. One was Bambu Lab A1 Mini 0.2 nozzle and the other was Bambu Lab A1 mini 0.4 nozzle. I selected the appropriate one and, suddenly, the whole AMS populated with what it truly had in it. I hope this helps some or if further explanation is required, I’m happy to go into more details. This was driving me crazy.
Agreed, especially when you google it, and see all kinds of responses of people having the same issue.
that is because ams and abrasive filaments is not compatible. cf stands for carbonfiber, if you had chosen non abrasive it would been accepted.
choose the correct profile for the filament and try again.
this solution does not work
Compiling a couple solutions from this thread. I ran into this but glad i found this thread.
The second option is resync assuming everything is correctly set on the AMS directly. The resync button is right of the minus sign.
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That has driven me nuts to no end. I ended up just selecting the filament from the dropdown box, making it all the same and then it allows me to select the one i want in the send dialog box. It’s the only way I’ve been able to use both PLA and PLA-CF or ASA in the AMS without removing them
Yes this worked for me too - Had PLA in slots 1,3,4 and PETG loaded in Slot 2 via the printer. Slot 2 would load and unload fine via the touchscreen however when I’d go to print, I could only select the PLA slots even tho in the slicer I’d selected PETG process. If I changed all 4 slots in Studio to PETG, Slot 2 became available to print from - Must be some sort of bug in the software, pretty sure previously I never had this issue so likely a firmware update has broken it either on the Studio software or the printer itself.
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I’ve been going around and around with my P1S and cannot get the AMS to change filament types and colors to match what I have in the setup in the ‘Prepare’ tab of the slicer. I’ve tried everything that has been discussed in this thread short of deleting and reinstalling the software as mentioned. Occaisionaly the AMS will randomoly get it correct when I changout filaments but sometimes it doesn’t like tonight. However, after messing around with things for a couple of hours I tried the Handy app. Change the filament type and color through the App and it went right through correctly in the Device tab as well as the Prepare tab in Studio. Go figure.
I can’t believe it was that simple! 
Thank you!!!
Found a solution, frequent problem for me, as I mix Bambu filaments with other brands frequently, trick is to go into Device tab, go down to bottom and do AMS Mapping, select the edit icon, looks like a six-sided hexagon button, with circle in its center, then you will see a pencil icon on the filament slots, click on it and you will be able to select a profile, and this fixes the problem (does not list custom profiles for some reason, but I just selected closest Bambu profile and ran with it).
This issue hands down as been my biggest problem so far, hope this helps someone else.
I power cycled my router and all in good.
This happened to me. Easy fix! I fixed it in Bambu Handy. I just changed to roll to PETG. When I went back to Studio, it worked.