Seeking Help: Bambu Lab P1S Filament Retraction Issue (HMS_0700-4000-0002-0004)

Hey everyone, good afternoon!

Could you please lend a hand? I've tried everything, but I just can't seem to solve this problem, and I'm really stuck.

I have a Bambu Lab P1S that's less than a year old with very few print hours. Everything was working perfectly. However, I didn't print anything for about two months. When I turned it on today, I initiated a print, but the filament wouldn't pass through the buffer; it seemed clogged. That's when I decided to investigate.

Upon checking, I found a broken piece of filament inside the buffer(that white part with a spring behind the printer).

That was straightforward enough. I removed the buffer, unscrewed a few screws, found the filament piece, removed it, screwed everything back together, put the spring back in, and reinstalled the buffer. Easy.

After fixing the buffer, I started a new print, and now a new, baffling problem has popped up.

The filament leaves the AMS, goes through the PTFE tubes, passes the buffer normally (the previous issue I fixed), and then reaches the extruder. It stops for about 2 seconds and then retracts completely, as if it were clogged. Initially, I thought it was a clog, which I know how to clear.

However, when I checked, the extruder is completely normal. I performed manual tests: I heated the nozzle to 220°C, manually pushed the filament, and initiated an extrusion, and everything worked perfectly. There's no clog or any apparent issue with the extruder.

So, what could be causing this? The filament reaches the extruder and simply retracts, it does it for 3-4 times before give me an error, even though there's nothing clogged there. I've checked everything and can manually extrude filament without issues.

The error I'm getting is: HMS_0700-4000-0002-0004: The filament buffer signal is abnormal; the spring may be stuck, or the filament may be tangled.

I've already looked at the spring in the buffer, and it appears to be normal.

Any ideas on what this could be? Your help is greatly appreciated!