Hi !
i came to hit a strange bug with dynamic obstacles, when an obstacle moved, the nav mesh has to rebuild the area, so it discard it, but never rebuild it…
at runtime :
By luck, i found that if i make the area to be rebuild in editor and try again, it does work (only for this area, other still buggy) , and after rebuilding the full mesh, everything works again.
The nav mesh rebuild is buggy on one of my coworker computer, so we disabled the auto one, and only i rebuild it from time to time, so the mesh was few weeks old ( but it was already a 4.17.2 one ). so the lvl had changed a bit, but not that specific part of the lvl
So i’m not asking for a fix as the workaournd is good enough and 90%+ of people probably have auto nav mesh generation. But just posting this so you guys know it exist, and if somebody has the same problem he doesn’t loose half a day thinking he broke something 
have a good day ! 
Additional infos:
-c++ project, 4.17.2, from luncher binaries
-my “runtime Generation” Setting is “Dynamic modifiers only”
-it does work on an other smaller test map in the same game with similar settings
-it does work if i set Runtime Generation to “Dynamic” but i don’t want a full rebuild of areas