Browser + version: Edge, Version 101.0.1210.53 (Offizielles Build) (64-Bit)
If you change the view to settings and come back to the overviews, only an ID is displayed for some entries for customer. If you refresh the browser, everything is displayed correctly again.
I had the same problem when updated to 5.1. I have the same infrastructure and i fixed it making a rebuild of elasticsearch.
The command is: zammad run rake searchindex:rebuild