How to export navmesh to make sure zone's groups length = 1

[yaoyutian]

After Pathfinding.createZone ,zone's groups length greater then 1;
while start position and end position in different group, findPath Failed!
after reading src code ,i still can't figure out why a simple mesh atfer createzone ,get multiple groups. can anyone help!
how do I need to do the exportation of nav mesh , can make zone group's length =1？

mesh file (change Filename Extension from txt to glb)
3-3.txt

[donmccurdy]

The mesh topology needs to be very clean to be used as a navmesh. Projects like 'recast' (previously available in Blender) did this automatically, but it's necessary if you're building the navmesh yourself too. Doing a 'merge by distance' in Blender might help, try the file below?

navmesh.glb.zip

It's also generally a good thing if the navmesh has roughly similar sizes of triangles, long/thin triangles may cause weird pathfinding choices.