Bubbling in the plastic coating on a mug press.

Hi, has anyone experienced this? a bubbling in the plastic coating on a Freesub machine from Dye Sublimation Supplies. I have no idea what's caused it any ideas? it has only affected one cup so far, I noticed it when checking it over last night before sublimating. It didn't affect the next mug that went in however. Any clue if it's fixable??

Edit: Should only say I only purchased it at the beginning of the month in a start up kit.

https://www.dyesubforum.co.uk/vbforu...tid=5155&stc=1

suggest you might be clamping the mug too tight, ... really don't need much pressure at all.
BUT
this ripple might effect results...

All our element blankets have some of this going on, and they perform fine