We recently upgraded our rails app from rails 4.2, ruby 2.3 and mongoid 5 to rails 5.2, longoid 6.4.2 ruby 2.4.4 and mongo 2.7.0. Since then we notice random Mongo::Auth::Unauthorized error. It doesn't happen often and doesn't appear to follow a pattern, it's totally random.

The mongoid.yml is relatively standard (please find it attached) and our puma.rb reload the config after each worker boot (attached too).

I spent a lot of time online looking for similar cases and couldn't find any. Any help would be great.

Thank you for your help and you open source softwares !