When I upgraded from v7.19.6 to v7.20, unfortunately, many PPPoE clients couldn't dial into my MikroTik router. Not wanting to keep my clients waiting too long, I reverted to v7.19.6. I haven't yet tried upgrading to v7.20.1.
... and ...?
Suspens in the Hitchcock's style 
Please provide the necessity of upgrading.
Well, albeit a hack with multiple instances, but BGP ECMP (new feature) is one reason. New features often neccessitate the need to upgrade, but upgrading at the cost of breaking everything else… I’ll personally pass.
Irritates the living daylight out of me that they BREAK things that has worked absolutely fine for years. 7.20x has just proven to me that Tik doesn’t do any kind of testing.
I always routinely upgrade to the latest version, but this time I didn't, and I was forced to downgrade to the previous version, v7.19.6.
It is very kind of you to communicate about your normal routine and how this particular release broke it, but your routine is evidently in violation of Rule #10, JFYI:
Particularly in the case of deploying a new release to several devices in use by clients, it is not a very good idea to update to a latest release before having tested it thoroughfully, 7.20 and 7.20.1 appear to be particularly "bad" (in the sense that they have given more problems than usual) but the general principle for software in production is to privilege (known) stability over (unknown) "better" features.
If you prefer, there is always a (small or large) risk of breaking something when doing changes, if you change things often, you are maximizing this risk, and before or later you will be bitten.