I'm back!
In mid-January, the VM hosting social.uhoreg.ca, hosted by Google Cloud, was taken down for "policy violations". Their support was extremely unhelpful, and they would not tell my what the issue was. It looks like their support can only send canned responses because they would re-send me the exact same messages after I had responded to them. My best guess as to the issue is that it was github.com/friendica/friendica… and so I've applied the patch for that (I'm having issues upgrading to the latest release, but that's a separate thing). In fact, the main reason that I found out about that issue was due to a report that I got from Netcraft at around the same time as Google suspending my VM.
I don't know if Google's support is better if you're paying them real money (I'm just using their free hosting tier, so I only pay a couple dollars a month for bandwidth), but Google support was pretty useless at providing me with any information or help. Even though their messages kept saying that I could ask for assistance, they were entirely unhelpful. In fact, the only real information that they gave me was the time of the violation, and the fact that the violation was reported by a third party. I got more information from an automated notice from Netcraft (who I don't pay any money to), than I got from trying to deal with Google Cloud support.
Eventually, I got a message saying that they reviewed my information, and they decided to reinstate my VM. (They didn't by the way. I had to contact them again and tell them that my VM was still disabled.) Still no information about exactly why it was suspended in the first place. Which means that I hope that it was just friendica#13216, and not some other vulnerability that allowed someone to take over my VM.
In summary, I highly do not recommend Google Cloud. I will probably be looking into migrating my ActivityPub home elsewhere. Which may involve switching software to something that uses PostgreSQL so that I can run it on my main VPS. Bonfire looks interesting.