Understandable. I noticed other people having issues with remote builders. It seems like there was a problem on Fly’s end and they reported they’d fixed it:
However you are still getting an error. Of course you could be getting a different, unrelated error with remote building … but the timing suggests it is related.
Do you have any request ID shown? Seems like Fly want that, at least based on that other thread. In the meantime they do track these forums so hopefully they should get back to you.