this sounds like the same issue someone reported in this thread. the “Auto” model selection seems to pick models that don’t always respect the ask/plan mode boundaries.
not sure if this is a fix, but one thing that’s worked for me when a model loops is just starting a fresh chat. once it gets into that loop state, the conversation history seems to make it worse. also worth trying: when you’re in ask mode, start your prompt with “don’t edit any files” just to reinforce it. annoying but it helps until they fix whatever’s going on with auto mode.
interesting that switching to Sonnet 4.5 Thinking worked. might be worth reporting which model Auto selected when it looped, if you can see it in the usage log.