This issue has been closed as 'Won't Fix' due to an extended period of time without updates. If this issue is important to you please let us know by posting on the AnswerHub or UDN, and Epic will re-open the ticket for further review.
Nav mesh is still affected by a nav modifier volume when added to a sublevel and then the sub level is removed.
Topdown character will not move into the space affected by Nav Modifier volume so not a rendering issue
Result: Nav mesh is still affected by the Nav Modifier Volume
Expected: Nav mesh reverts to its original state
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-37291 in the post.