The PC runs 1.8.0; The iPad runs 1.8.0; The Switch runs 1.8.1; No updates are available for any system.

Playing on a local (home) network.

If the PC hosts, the Switch and the iPad can connect.

If the iPad hosts, the Switch and the PC can connect.

If the Switch hosts, the PC can connect on the 3rd or 4th try, and the iPad can't connect at all.

More specifically, the iPad gives a "disconnected from server" error and the game says "blah has left the game" but the iPad player never left the loading screen and the Switch player never saw the iPads avatar appear.

This was a Christmas gift, specifically to allow cross platform Minecraft gaming.