NavMesh in two different levels

Hi there, I have the problem again…
I’ve made some changes in my game (I added some IA characters walking around, using the same navmesh as the player), and the move is only possible in one of the 2 levels now.
I’ve tried a lot of things (force rebuild on load, dynamic navmesh, using navquery in the player pawn…), but nothing works. Sometimes it works in one level, sometimes in the other.
Has someone an idea ?