We have been able to reproduce this issue with your information. It seems to be a bug with the OpenProject Documents plugin, which seems not to be making the CSS available when precompiling assets.
To fix this, please execute the following commands (supposing
INSTALLDIR is the installation directory):
$ cd INSTALLDIR/apps/openproject/htdocs
$ mkdir -p public/stylesheets/documents/
$ cp vendor/gems/openproject-documents-5.0.17/app/assets/stylesheets/documents/documents.css.erb public/stylesheets/documents/documents.css
I hope it works!