If the bottom end of the PTFE has deformed at all, you'll get weird clogging issues as the flow is not smooth.
Note: For changing between ABS and PLA, I find Laywoo-D3 wood filament good as a transition filament. You need at least a 0.4mm nozzle else the wood particles tend to clog it, but since you're using 0.5mm, it should work fine. It extrudes well at ABS and PLA temps, and it's easy to see when it's all cleared out (the plastic stands out against the wood).
Start at ABS temp, Remove ABS and insert Laywoo-D3, extrude till clean, change to PLA temp, remove Laywoo-D3 and insert PLA - Any remaining Laywoo-D3 will extrude easily. You can also do the reverse.
Definitely avoids little pieces of ABS not melting and clogging things.
Note: For changing between ABS and PLA, I find Laywoo-D3 wood filament good as a transition filament. You need at least a 0.4mm nozzle else the wood particles tend to clog it, but since you're using 0.5mm, it should work fine. It extrudes well at ABS and PLA temps, and it's easy to see when it's all cleared out (the plastic stands out against the wood).
Start at ABS temp, Remove ABS and insert Laywoo-D3, extrude till clean, change to PLA temp, remove Laywoo-D3 and insert PLA - Any remaining Laywoo-D3 will extrude easily. You can also do the reverse.
Definitely avoids little pieces of ABS not melting and clogging things.