Hey there @Haugie46! There can be a myriad of issues why a map won’t save. Some of the most common are:
Having more than one instance of the editor open (It’s forcing access on the file)
Having another program open that’s accessing the umap file (some source controls can trigger this)
Path name for the map is too long (though it mentions it in the output of the console when this is the case)
Are there any other warnings in the console when you go to save the map?