Did this a few patches ago closer to release based off other user posts with similar issues of fuel consumed and no orbit change and that seemed to be the case with methalox engines as well. I can't tell you the exact value for designing ships to not have this issue but for the case of testing earlier i changed the thrust limiters down from 100% where warp was fine to around 5% it created the bug above with time warp. Maybe Devs can give a better answer to around when it is seen so you can design towards the limit? In the meantime i avoid the Ion engines and am careful for TWR of hydrogen cores for longer missions
