Hi @mspriggs, welcome to the Glitch forum, and sorry for the bother!
I can currently load that project just fine, and while that doesn’t tell us anything much about what might have been happening when you were encountering the issue, this has the feel of a network issue to me, particularly the invalid cert issue. That often points to some anti-malware solution running somewhere on the network that’s connecting to Glitch - we’ve seen this in school environments a few times, for instance.
If you have another network you can try (cell data if often reasonably accessible if you have a mobile device handy) that’s one way to find out if the problem is network-specific