I also have a constant connection error to cloud backup but only from one of my router. All the other have no problem except the usual temporary service failure that we all noticed on cloud backup once in a while.
From the problematic router I can ping cloud2.mikrotik.com, the mikrotik ddns service works, the download and upgrade of new firmware works too.
There is nothing in my firewall rules that would block output connection from the router.
Any ideas why this specific router would have constant connection error?