For soldered BGA dog-bone pads, that is a major issue, common within the industry. If the soldermask strip between the via and the BGA pad is too small, there is not enough adhesion and the molten solder runs right under the soldermask strip down into the via hole. Too thin of a strip of soldermask allows solder thieving from the solder ball. But for unsoldered vias not connected to a soldered pad on the opposite side, I cannot imagine what issues there would be. Soldermask is not considered an electrical insulator, so if a designer was depending on a thin sliver of mask to provide insulation between two vias of different potential, shame on them.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
Sent: Tuesday, February 19, 2019 9:58 AM
To: [log in to unmask]
Subject: [TN] soldermask silvers

In my experience, what a PCB fabricator would consider a sliver would be
the strip of soldermask material between RECTANGULAR pads being less than a
minimum width.
We got a "DFM report" for a board where minimum distance between ROUND vias
is being reported as slivers.Has anyone ever heard of problems with minimum
mask material between round, unsoldered vias?
I can't imagine any real-world problems that could cause, but I have an
open mind...