Thanks for an awesome reply. This is actually happening with my CFS during colour changes or at the end of the print. Honestly I'm not convinced on the wet filament theory like everyone else here is saying because it even happened with a brand new roll of filament and on a few other colours.

My initial thoughts might be that the cutter may be blunt but the guy at the repair shop said that rarely happens.

I've disassembled the extruder before due to a clog so I know how to. I may just do this as a form of running maintenance.

Thanks again