I had been ignoring this thread because I assumed it was just my wifi network (AC1900 WIFI but a fair distance through numerous double-brick walls). I'm starting to wonder otherwise now, after reading this thread more thoroughly.
Right now I can't go more than 3 days without getting that message. If SD content I can usually (but not always) just pause for a few seconds, then play again and all good. If HD content though I usually need to reboot either the router or ATV4.
I'll try changing the setting to direct streaming and see how I go. I don't use chapter markers so I won't miss them. See if I can go a week without this message.