middlewared runs for days, sometime two weeks, and then abruptly uses up RAM until system is not responsive. Restarting middlewared usually clears up the situation.
In the current running case, it's not the main middlewared that's growing without bound:
root 52507 0.0 38.8 146449392 104070560 - I 16:12 97:07.13 | `-- python3.7: /usr/local/bin/python3.7 -c from multiprocessing.spawn import spawn_main; spawn_main(tracker_fd=13, pipe_handle=75) --multiprocessing-fork (python3.7)
These folks are not using replication. Instead they are using rsync tasks. This is the only thing that is unusual about this system so far.