after upgrading from redmine from 3.0-stable to 4.0-stable, redmine started throwing intermittent failures:

ActiveRecord::ConnectionTimeoutError (could not obtain a connection from the pool within 5.000 seconds (waited 5.005 seconds); all pooled connections were in use):
  app/models/setting.rb:235:in `check_cache'
  app/controllers/application_controller.rb:90:in `user_setup'

journalctl shows this error:

SIGPIPE: writing to a closed pipe/socket/fd (probably the client disconnected) on request /issues/227>
uwsgi_response_writev_headers_and_body_do(): Broken pipe [core/writer.c line 306] during GET /issues/>

i tried increasing the number of rails db pool connections and timeout, but that did not seem to help