Corrupt Streaming level (sublevel)

One of my sub streaming levels has i believe become corrupt, it has gone red in the levels window and says it has 0 actors, i have tried deleting it and even re populating that area again but once i saved closed and re opened it got corrupted again, and i can’t even see the that sub level in my content/maps folder anymore, i tried adding one of my backups to the folder but the same thing keeps happening. does anyone know how i can fix this issue as its rather annoying to have to repopulate a whole area again.

Still don’t know what caused the problem, but i have used a backup to restore the selected level but this time i not longer renamed it back to what it was to begin with now it has a time and date in the name but at least it works fine.