This is the exact same issue I have been experiencing, along with someone else, and am pulling my hair out too. My brand new printer has turned into a paper weight because all I use is PETG. Nothing but failed prints.
Tell me, did you update to the new slicer version, 2.3.1.51? As it seems the slicer is not passing over some settings correctly, after Bambu disabled and made updates to the app making some past settings now read only.