I dont like necro’ing an old thread like this, however, this pops up in a search for this issue so… I’m linking one solution to the issue in another thread : Answer here : :
Basically, raise the “Cell height” in your navmesh resolutions. Normally the “default” resolution should be enough to change. I raised mine from default 10 to 20 for example due to very tall mountains in my level.
Hope it helps someone else.
Edit: of course, make sure to begin with that your navmesh volume DOES encompass the area you need navigation in 