nav mesh assistance

Could someone possibly send me the direction to learn more about nav meshes?? Some of my AI is just getting stuck and not moving…
I have it over my landscape and it’s pretty rigid but…it seems like it’s covering all of the ground…

They’re bats. They fly above ground and honestly the work fine usually but I have a spawner they come out of and they get stuck sometimes and I have no idea why.

Thanks everyone.