I had the same error. I posted a detailed bug report to the OpenAI Help Center, but I don’t think any humans actually saw it. After a few weeks I finally got a response, but it asked me to clear cookies/cache and share a screenshot. My bug report said that I did that and had screenshots.
Anyway, I had to make a whole new GPT. Hopefully it doesn’t happen again.
Suggestions: be sure to save your GPT’s prompt in version control, and don’t distribute your GPT’s url. Instead, get a custom domain and redirect to your GPT. That way, you can delete and remake your GPT without too much disruption to your users.