We don't throw any 513 errors in CB. I'm not aware of any existing in Joomla either. Enable debug mode and maximum error reporting in Joomla global configuration then retry and provide the full error output.
I've downgraded to pkg_communitybuilder_2.8.0+build.2023.08.10.17.13.31.fc304074a version, and it's ok.
The things that changed between your release and latest are as follows.
1. Additional substitutions for custom profile layouts
2. System fields in CB > Field Management can now be unpublished
3. Fixed a type casting issue in CB Forums Kunena user fields synchronization
None of these should have any impact on login.