When I place a map in an item frame and then relog, the map doesn't load and the item frame appears emtpy.

You need at least 2 players to reproduce.
1. Pick a random location, create a map and place it in an itemframe
2. Delete the map item from your inventory
3. Player B stands next to the map, the player A relogs
4. Player A sees the item frame empty

When player A now holds the map in his hands again, the map will load correctly.
When you load a chunk with an item frame in it, it will also load the map for all clients. This happens when you enter or join in an unloaded chunk (no player is in there).