Reproduced on ovh (1.12 forge) and hetzner (1.8 forge and 1.15.2 vanilla) with 3 different users on 3 different servers.

These people can play for a couple seconds to hours (randomly), then "timeout" for about 30 seconds where they dont see other players move nor do other players see them do anything and then get disconnected with "java.io.ioexception, external host broke the connection" (translated from dutch as i can't find the english ticket at the moment)

We tried everything from resetting routers to using wifi/cable but nothing helps, these people all have a stable network connection. This only happens to specific people while others on the same server can play fine.