I have DC (android version 1.44.0 from f-droid) configured with 4 different accounts, one of them is a test account but since shortly, hopefully, going into production the test server has not been updated/cured anymore and the certificate has expired, fairemail and k9-mail have notified of the problem with a notification, DC has not but if I go into the information regarding the connection I find the error reported.
In my opinion DC should still notify me of any connection problems as several xmpp clients do (like conversations and its various forks) or like k9-mail and fairemail, because since it is not my main account and I use it very little, if I had not configured it as well on other clients I would not have noticed the problem until I opened it on DC.
The same thing should happen with the desktop version (I have 1.44.1) and possibly ios (which I do not use).