How to pick up .umap? How to make it visible in Content Browser?

The problem is .umap-file does not picked up by Content Browser (CB), however, it is picked up by UE.

• E.g., I can not create new Level with the same name, or [when I change Editor Startup Map] UE says «Failed to open map file. This is most likely because the map was saved with a newer version of the engine», but the version is the same.

• I looked for answers first… tried to copy .umap-file in different directories (Examples/Templates/Content Packs/Project’s Content folder(s), etc.), but the result was the same, .umap-file was showed in Content Browser.

• Another problem is this .umap-file just disappeared somehow from the current project’s CB (but it is still in MyProject/SomePacksHierarchy/Content/Maps or just …/Content/), i.e. yesterday it was in CB, I saved Level, turned off the OS-session (win 8, win 8.1, win 10), and now there is only a headache.

Is it possible to import .umap somehow in CB? Maybe, I should write some flags in file manually in Hex Editor?.. Or should I override any .cpp-files in my project to pick up .umap?