A chunk of filament got stuck in the extruder. It was such a large chunk that it even reached the filament sensor.
Once those pieces were removed, the printer worked fine but only from the external spool holder.
The issue comes with multicolor printing.
It starts printing without issues with the first color, but when it needs to switch to the next one, it throws an error.
If it doesn’t throw an error in the CFS, it throws one in the buffer.
Following the guide from the wiki, I proceeded to disassemble the bottom part of my two CFS units to look for traces of filament, which I didn’t find. So, I cleaned what was already clean, so to speak, and put everything back together. Both units still don’t work.
Taking advantage of the fact that the extra CFS I bought came with an additional buffer, I swapped it out, and the errors persist.
When canceling the print, there’s no issue retracting the filament from the screen, and it doesn’t show signs of being damaged.
Honestly, I don’t know what to do anymore. So, I’m turning to your wisdom 
.