I use Tvheadend 4.3.0~pre+201911281811-0, but I tried with 4.2.9 the problem is the same.
So I use iptv automatic network, m3u sources from different provider, therefore it's possible that one or more muxes will die.
We use this tvheadned with 5 persons, if somebody try to play a died channel, then all active channels will restart till he do not close the playing of died channel, so if i watch tv at that time, several times it restarts.
Here is just an example for the log:
2020-04-08 17:14:52.276 webui: Stop streaming /stream/mux/0c8dabfd6fc748af0ecd4c4ded37abba?auth=PpmQguw8g6Sa6Tv0RQcj7cP3swX4, timeout waiting for packets
2020-04-08 17:14:52.276 subscription: 0094: "HTTP" unsubscribing, hostname="::ffff:.........", username="szalkaijozsi", client="Lavf52.104.0"
2020-04-08 17:15:02.280 subscription: 00CC: service instance is bad, reason: No input detected