We’re not talking PLA, we’re talking flex which will use any excuse not to extrude properly. I was told to do the pull test by Micro Swiss technical support and I was surprised at what came out of the nozzle at the end of the filament.
You should see notches on your flex (just like PLA) - you may need to increase your tension for it.
I have gotten some amazing models printed with flex but it’s a real pain in the ass to work with.