Redmine

Using the official docker image I recently updated from 4.0.3 to 4.2.0, no plugins installed (anymore).
Database is on mysql:5.7

Since then new accounts and some existing users (2 out of 30) authenticating using LDAP started having issues logging in. Internal accounts work fine.
LDAP authentication works fine for everyone else.

@I, [2021-04-20T15:46:52.874309 #1]  INFO -- : Completed 500 Internal Server Error in 22ms (ActiveRecord: 3.1ms),
F, [2021-04-20T15:46:52.875489 #1] FATAL -- :   ,
F, [2021-04-20T15:46:52.875538 #1] FATAL -- : FrozenError (can't modify frozen String: ""):,
F, [2021-04-20T15:46:52.875567 #1] FATAL -- :   ,
F, [2021-04-20T15:46:52.875601 #1] FATAL -- : app/models/auth_source_ldap.rb:250:in `force_encoding',
                    app/models/auth_source_ldap.rb:250:in `get_attr',
                    app/models/auth_source_ldap.rb:199:in `get_user_attributes_from_ldap_entry',
                    app/models/auth_source_ldap.rb:236:in `block in get_user_dn',
                    app/models/auth_source_ldap.rb:232:in `get_user_dn',
                    app/models/auth_source_ldap.rb:59:in `block in authenticate',
                    app/models/auth_source_ldap.rb:144:in `block in with_timeout',
                    app/models/auth_source_ldap.rb:143:in `with_timeout',
                    app/models/auth_source_ldap.rb:58:in `authenticate',
                    app/models/user.rb:344:in `check_password?',
                    app/models/user.rb:244:in `try_to_login!',
                    app/controllers/account_controller.rb:311:in `password_authentication',
                    app/controllers/account_controller.rb:306:in `authenticate_user',
                    app/controllers/account_controller.rb:40:in `login',
                    lib/redmine/sudo_mode.rb:61:in `sudo_mode',@