PETG is picky about layer heights and speed.

Thick and slow for PETG. I usually double my layer height vs what I would print in PLA. With my .6 nozzle I print with .3 layer and cut my speed down to 50% for the first layer. Since you said it happens mid print you might be printing too fast for the first few layers and it is getting too high because the layer is not cooling enough and it starts curling. You can also try reducing flow if your nozzle is worn and it’s allowing more plastic than the sclicer expects which will cause too high layers and scraping.