I have a KolabNow account, which I access with Kontact. It is set up in Akonadi as a "Kolab" account, default arrangement of folders etc. A couple of days ago the mail folder disappeared from the KMail folder list, and the calendar and contacts likewise disappeared from KOrganizer and KAddressBook. However, the account still shows up in the list of Akonadi resources and in Settings->configure KMail->accounts. Eventually I gave up, deleted the resource in Akonadi, created a new Kolab resource, and downloaded all my mails etc again. After a couple of days of working normally, the problem has now recurred, exactly the same as before - my account shows up in the list of Akonadi resources but the contents do not appear in KMail, KOrganizer etc. After looking at a couple of similar bugs on this site I tried disabling serverside subscriptions and switching various other account options but nothing helps. The only clue I have is that, when I click "Check Mail", the progress box that pops up from the bottom right of the KMail window briefly shows the error "Unable to append mimetype for collection KolabNow resourceId: 17" Reproducible: Sometimes
This bug has never been confirmed for a KDE PIM version that is based on KDE Frameworks (5.x). Those versions differ significantly from the old 4.x series. Therefore, I plan to close it in around two or three months. In the meantime, it is set to WAITINGFORINFO to give reporters the oportunity to check if it is still valid. As soon as someone confirms it for a recent version (at least 5.1, ideally even more recent), I'll gladly reopen it. Please understand that we lack the manpower to triage bugs reported for versions almost two years beyond their end of life.
Just as announced in my last comment, I close this bug. If you encounter it again in a recent version (at least 5.1 aka 15.12, preferably more recent), please open a new one unless it already exists. Thank you for all your input.