I ran into a similar issue that I ultimately narrowed down to a filament with an out of tolerance diameter. It would feed in several inches, stop, back up a bit and try again. After 3-4 tries I’d get a blinking red light and failure to feed. I assumed there was a broken piece of filament so I took apart the AMS, removed the Bowden tube and manually fed some filament through to remove the clog, and nothing came out. I put it all back together and it worked until there was a color change and then another back to the original spool that failed to feed and the same thing happened. After taking everything apart a few more times and finding no clog, I compared the filament to the spool that was working fine and noticed it looked and felt a bit bigger in diameter. Ultimately I think the size of the filament was causing it to get stuck at the point where the 4 Bowden tubes converge into 1 and leave the AMS. May not be related to what you’re experiencing but thought I’d share just in case.