Some R-groups end with many conformers that are identical - Symmetry Issue?

[bieniekmateusz]

This happens when adding this R-group:
'*C(=O)N(C)C'

Specifically, potentially the methyl groups get mixed up, and different methyls correspond to each other, even though they occupy exactly the same 3D space.

So these conformers have a large RMSD and are therefore seen as different.

Thanks @AsmaFeriel000