Blender (2.9): Vertices invisble, unselectable. Very strange problem

Since using the latest Blender build (2.9) I have been having some weird geometry artifacts:
sometimes the vertices are gone/disabled and while I still can delete/select the faces any other oction will not properly work.

If I connect other faces to this “broken” mesh they will inherit this problem as well. Does anyone know what is going on ?
EDIT if I re-import as an .obj the mesh works fine. Strange isn’t it ?

One suggestion is in edit mode … Select all and Cleanup>Merge by Distance…
You may have doubled vertices which make things like this happen…

Other than that…would need to see the file if you wish to share it…