Safari log on problem on ipad

I have my browser passwords stored in my iCloud Keychain and that had been working great across all my devices until last week. I tried to log on to Thingiverse using Safari on my iPad and got this and have ever since:

Bad Request

Your browser sent a request that this server could not understand.

Size of a request header field exceeds server limit.

Apache/2.4.7 (Ubuntu) Server at 10.250.55.3 Port 80

Interestingly, the stored Thingiverse password works on the iPad with Chrome and with Safari on my Mac