I was playing 3 player splitscreen on a Nintendo Switch in docked mode.  All 3 players were in the same village.  I noticed a pillager scouting party and killed all but the captain.  I then warned the other 2 players to get ready for a raid.  They quit the game and then one joined back in.  I then killed the captain and a raid began. 

At first the raid bar filled and there were periodic horn noises from the pillagers, but we could not locate the pillagers.  Eventually even the horn noises stopped.

Soon one player left and it was again a single player game.  I was not able to locate the pillagers, but I noticed unusual behavior with ice that had been frozen using frost walker boots.  I tried to break the ice and all it did was break the sand blocks beneath the ice.  I assumed something was wrong with the raid so I moved a few hundred blocks away, saved, and quit.  The saving worked normally, but after this any attempt to load the save file failed.  On the Switch, the game crashes with "The software was closed because an error occurred."

I created a realm with this file and I can't load it either, from a Windows 10 PC or the Switch, and with my own user or an invited user.  My Minecraft username is Grim6ergen and the realm is just called Grim6ergen's Realm.

Finally, I downloaded the world onto a Windows 10 PC and it also causes the game to crash.  I've attached a Windows Error Report .wer file.

The world files are still viewable (and the various built things look intact) in 3rd party editors like MCC ToolChest PE and Universal Minecraft Editor.  This world was never modded in any way and was previously only on the the Wii U and then the Nintendo Switch.