The solution is simple; execute this SQL to delete the invalid rows:

DELETE FROM exp.PropertyValidator WHERE TypeURI = 'urn:lsid:labkey.com:PropertyValidator:length'

The "length" validators were created long ago, but are no longer valid. These rows should have been deleted by the upgrade process back in 2021. Somehow, your server skipped that part of the upgrade; this could happen if the server was shut down part of the way through a past upgrade. Please let us know if this fixes the problem.

Separately, I'll look at making the code resilient to unrecognized validators; we definitely shouldn't block server startup.

Adam