In the past cases of "400 Bad Request" are due to buggy browser extensions, VPNs, or security software, that interfere with the network requests the browser is making, and ends up making them invalid. In particular the error beginning "YIkPfp2E9gyQ09dk_yNy9scwlvKH58Ft..." does not look like a request Construct would normally make. So I would guess this is not actually a problem with Construct.
If you disable browser extensions/VPNs/security software, you may need to also clear your browser cache afterwards to allow it to start over properly - otherwise it may still be getting error responses from the cache.