Just adding another use case here with all the known problems. Thankfully there was help here as always (eventually after asking but always 
).
Using a DO 30G maybe 5 year old installation. Yes, I know that’s pretty much asking for trouble, I haven’t had time to even check out their last 2 year ago upgrade so…
Got the Discourse Currently Upgrading, could not reset it.
Cursed having to ssh in to fix things, and of course I had 24G used which did NOT free up enough using the usual methods.
Eventually found the autoclean and autoremove which gave me another 5G and then things got better.
Could those two perhaps be a question in the rebuild when you run out of disk space?
Anyway, I guess even docker upgraded as I had both upgrades waiting.
The only question here really is, why on earth did I even end up in some “auto upgrade”? I specifically upgrade with 3-6 month intervals depending on when I have time to sit here and figure out why things went wrong this time 
. Of the last four upgrades only one has gone through nicely (yes, did I mention disk space already lol).
End nag :
I simply want a running forum, one I can take care of from anywhere, without having to resort to ssh and public/private keys etc which I don’t have access to everywhere.
So a MS-style forced upgrade (even if there is a setting somewhere which I have NOT selected specifically) is a real no-no when the result possibly is a non-working forum when you get annoyed of the dashboard nags.
But never mind, I would not change this software to anything else. If nothing else it keeps my outdated Linux knowledge up to date a bit 
.