Normal maps in item frames causing lag and crashing server

Upon investigating why my friends realm was crashing I have found out that normal maps and locator maps lag and crash servers when placed in an item frame I had a total of 12 maps in each frame and it was causing the server to lag and crash
1:make the 12 maps and peice them together from 12 different chunks
2:place them in item frames
3:give it 30min-1hour and the server shows signs of lag and will sometimes crash causing you to loose about 50min-1 hour of work