This is the problem in a picture: https://prnt.sc/gkb57d
When I set a clumping modifier and then hit the xgen preview button i get the message:
// Error: XGen: No clump guides found. [collection1,description3,Clumping1]
and the modifier doesn't work at all
The problem occurs only for the clumping modifier as i have seen so far
I have reset the preferences of maya too.