Simple Scan crashes almost immediately upon start-up

I'm using simple-scan on Debian and it is now always crashing. It worked fine a few months ago. I suspect that something got upgraded (I'm running bullseye) and broke things. The output from simple-scan says:

simple-scan: thread-watch.c:165: avahi_threaded_poll_quit: Assertion `pthread_equal(pthread_self(), p->thread_id)' failed.
Abort

I tried running ldd /usr/bin/simple-scan to make sure all the packages associated with all the libraries are recent, including libc6. I also tried running with simple-scan -d, but the debug output proved useless. I also tried strace /usr/sbin/simple-scan to look at all the shared libraries that were being loaded and they all had recent versions. I noticed that the libavahi shared libraries are loaded dynamically (i.e., not visible via ldd) by simple-scan. So, I made sure that those were also recent. I also tried xsane, but it has the same problem. Perhaps unrelatedly, I see the following messages in my system log file:

avahi-daemon: Too many clients, client request failed.

scanimage does not crash, but it fails in an unrelated way. I am at my wit's end and don't know what else can be done.