Katz Ueno (known as Katz515 on the Concrete5 forum) faced the very same issue. He came up with the solution on how to fix this. For this, he created a Gist at GitHub.
But.. just in case the Gist will be offline, here is how to fix it (credits to Katz of course).
- Go to /concrete/controllers/single_page/dashboard/system/conversations/settings.php
- Add use Database; right after use Core;
- Replace Core::make('Concrete\Core\Database\Connection\Connection'); with Database::connection(); (found twice in this file)
Hope this will get rid of all your headaches!
Edit: This bug has been fixed in version 18.104.22.168