Yes.

This is the unfortunate thing about wrapping LLMs in API calls to provide services.

Unless you control the model absolutely (even then?) you can prompt the model with a well manicured prompt on Tuesday and get an answer - a block of text - and on Thursday, using the exact same prompt, get a different answer.

This is very hard to build good APIs around. If done expect rare corner case errors that cannot be fixed.

Or reproduced.