If you upgraded Docker, it’s still installed, and this problem appeared when you upgraded, then I’m pretty sure that rebooting will solve your problem. Note: Free advice is worth what you pay for it. 
Make a backup before you reboot. Worst case, with a backup and your app.yml you can spin up a new server and start anew in under an hour (unless you have 10s of GB of data, perhaps).
My plan would likely work for a number of hosting services.
If you’re super paranoid you could spin up a new server somewhere and pull a backup over there so if something went horribly wrong you’d have a fallback plan.