Elements of Map and Backround Layer Disappear

I have been having issues with elements such as doors, tables, chests and other such items on my map disappearing when I log back into my campaign. I have replaced these elements a couple of times each at this point and new ones are also disappearing.  My maps are by no means very large or involve a great deal of material per level. This is started on one page of my campaign's pages and is now affecting several.

I occasionally have items that don't appear immediately.  Have you waited a few minutes to see if those missing items appear late?

I had run into that problem before. It seems to be a different issue this time, as I have stared at the same page for approx. fifteen minutes now trying to use sheer force of will to make them reappear.

I checked beneath the maps first thing.