First encountered on Xbox One, additional weird behavior on Windows 10 with same world.
I have a locator map (zoom level 4/4) that I made copies of. I named the map on an anvil, and at first my player location was not showing on the map I was holding, though the placed locations were. The previous copy (before naming, still saying "Map 15" instead of "Home Map") did not show any locations.
I Exited and ran on Windows 10 version to grab screenshots more easily. Now my player position showed up, but a placed location did not. (see attached screenshot 1: player location is looking at a placed map, but that location is not on map in frame or held map.)
I then had a message saying I had disconnected from the server (perhaps due to this, perhaps due to alt-tabbing for screenshot editing) – upon reloading, all locations had disappeared from the placed "Home Map" and the carried map. (Screenshot 2: taken right after reloading, should be no state changes from screenshot 1)
This world is on Realms, pure survival (not ever switched to creative, can earn achievements)