Maps delete recently marked banners upon reopening world

I have consistently found that with the feature of marking banners on maps, my game seems to always delete recently made markers upon reopening my selected world with the maps. I currently have two map walls in my world, which all use 3x bigger maps, and I carry around the exact same maps with me so I can update them if needed. I don't know if any of those are the cause, but I figured I would list them. This may not be the worst bug, but I would appreciate a fix!