Build failed to start. The following error occurred: Cannot have more than 0 builds in queue for the account

I’m having the exact same problem. I asked the rate limit folks but so far they responded as though they didn’t even read the issue I mentioned. I don’t believe I should need to pay for support just to have a problem on their end resolved. You may have read about this on other sites. It sounds like a common problem that only AWS employees can remedy.