Cannot login due to InvalidHash

I use the omnibus package of gitlab-ce. Some days ago a prometheus database was broken, but i got that fixed.
But since then, when i try to login i get directly after entering username and password and before entering 2nd factor credentials a HTTP 500 Page.
All services are running, gitlab-rake gitlab:check RAILS_ENV=production says everything is okay. Restarting or reconfigure does not change this behaviour.

/var/log/gitlab/gitlab-rails/production.log gives:

Started POST "/users/sign_in" for at 2018-05-08 14:30:20 +0200
Processing by SessionsController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"[FILTERED]", "user"=>{"login"=>"xxxx", 
"password"=>"[FILTERED]", "remember_me"=>"0"}}
Completed 401 Unauthorized in 1019ms (ActiveRecord: 35.5ms)
Processing by SessionsController#new as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"[FILTERED]", "user"=>{"login"=>"xxxx", 
"password"=>"[FILTERED]", "remember_me"=>"0"}}
Completed 500 Internal Server Error in 84ms (ActiveRecord: 1.5ms)

BCrypt::Errors::InvalidHash (invalid hash):
  app/controllers/sessions_controller.rb:21:in `new'
  lib/gitlab/i18n.rb:50:in `with_locale'
  lib/gitlab/i18n.rb:56:in `with_user_locale'
  app/controllers/application_controller.rb:326:in `set_locale'
  lib/gitlab/middleware/read_only/controller.rb:28:in `call'
  lib/gitlab/middleware/read_only.rb:16:in `call'
  lib/gitlab/request_context.rb:18:in `call'
  lib/gitlab/metrics/requests_rack_middleware.rb:27:in `call'
  lib/gitlab/middleware/release_env.rb:10:in `call'

Hi there,
did anyone else catch this BCrypt::Errors::InvalidHash?

Currently struggling with debugging this on CentOS8 + Gitlab Omnibus 12.6.