Hey,
I just worked through a problem similar to what you are having. I was able to save most of my umap by loading up a backup. To do so go to Saved->Backup and copy your .umap file. Then go to where your file that is isn’t opening is saved, delete it and paste in the backup in its place. Make sure the backup has the same name as the file you deleted. It won’t restore everything but it at least will keep you from starting from scratch.