A bit over a week ago, this Friendica instance suddenly stopped receiving posts over ActivityPub. It took me a while to figure it out, but it turned out that my server's clock was drifting, and at some point drifted to be more than 5 minutes off, which caused issues with signature verification. So I fixed the NTP configuration on my server, and now things seem to be back to normal. I've missed about a week of posts, but I guess I'll survive.