If you only want a specific weapon fix, just delete the animation folders you don't want and use it as is. check the change log.

Changes all idle to the vert grip animation, to get rid of the hands not holding the weapon when it is lowered/moving when not using a vert grip (see images)

Esp version for those who still have the issue, the esp version might have the NPC bug, but not from my testing.

Another option is to use animations from another mod you have, it might look weird but it's worth a shot.