I was experiencing this on a large map (25 GB), which is why I am also convinced the issue is brought on by a too large file.
I have now downloaded the map and used MCA Selector to delete all chunks that hadn't been visited for more than a minute (useless chunks generated during exploration). Doing this on all three dimensions shrunk the file size from 25.6 GB to 1.9 GB (!!).
The trimmed map is re-uploaded to the Realm and perfectly functional. Backups are loading fine and there are no more crashes. Everything important on the map is still there and the file was just unnecessarily inflated. I am personally very happy with this bandaid fix.
PeterPanic
I was experiencing this on a large map (25 GB), which is why I am also convinced the issue is brought on by a too large file.
I have now downloaded the map and used MCA Selector to delete all chunks that hadn't been visited for more than a minute (useless chunks generated during exploration). Doing this on all three dimensions shrunk the file size from 25.6 GB to 1.9 GB (!!).
The trimmed map is re-uploaded to the Realm and perfectly functional. Backups are loading fine and there are no more crashes. Everything important on the map is still there and the file was just unnecessarily inflated. I am personally very happy with this bandaid fix.