What I expected to happen was...:
Placing maps within item frames on a wall should result in a seamless map "jigsaw"

What actually happened was...:
When initially placing the maps they appear to be one continuous map without any breaks or lines between them, however when logging out and back into the world the maps have a think white line between them until removed and re-placed

Steps to Reproduce:
Note: Will only work on Realms and BDS

1. Place down 2x2 item frames on any surface
2. Place 4 maps (can be the same map - preferrably filled in to show the issue clealy)
3. Note no interruptions at the map borders
4. Log out and back in to the world
5. Note the new lines around each map on each border.

Note:
Does not appear to occur (at least not with the same repro steps) on a Singleplayer world. Can however reliably reproduce (with every log out) on a Realm or BDS install. May also be related to the maps having a pink and black checkerboard briefly when logging in.

Apologies for the alerts watchers, struggled to update this one on my phone