Have that also at random. Sometimes I just leave the harbour, sail a few shiplenghts, and out of a sudden, no movement of the ship, but Ingame-chat, -map, -menus, discord, ts continue working. Restart of the game necessary or waiting a couple of mins till the screen "entering open world" appears.
Happens often 5 or 6 times in an hour while in OS or instance, which makes tags or fights not really enjoyable... Sometimes no problems for hours, even when my 2 boys are playing with me on our slowcoach-internet-connection
I do not have this with flightsims, even in the biggest furballs with planes and bullets everywhere.