kmaxatI might have found a solution to the chattering issue:
I just disassembled my V60 because two keys were chattering. (you can remove the top of Matias/ALPS switches without desoldering or unmounting the switch from the plate:
)
I discovered that the Quiet Pros were apparently lubricated by KBP using a transparent grease. It seems like too much of this grease was applied to the chattering switches, it made contact with the copper plates inside the switch. I removed the grease, cleaned the copper contacts and they are no longer chattering!