Hey Phil,
This forum isn't generally meant for 1-on-1 technical support, but I recognize that you don't really have enough info or enough ideas of next steps in order to create a good stackoverflow question or public issue tracker issue. That being the case, why don't you go ahead and capture a
HAR recording of your attempt at creating the project, and see if you can use the HAR analyzer to see any extra error detail in HTTP responses. If you manage to find enough information to determine the issue, or even if you can just produce the HAR file, create a
public issue tracker issue with that attached, set it to "Type-Production", and post the link here so that I can follow up with you. While we don't do 1-on-1 technical support here, if you've noticed a problem with the platform itself, we definitely want to help fix that.
Finally, it's possible the rate-limiting response is perfectly normal and you're attempting to create projects at a fast rate (it seems you'd be aware of that, though). So, that's something to consider.
Anyways, let me know how it goes, and I'll be able to advise you on next steps,
Best wishes,
Nick