Thought I'd offer this up here to people smarter than me: I recently installed a vessel sink with overflow during a bathroom remodel, and while the drain (with overflow) seems to be installed correctly (no leaking underneath into the sink cabinet, along the pipes to the p-trap, etc), after the water flows for a bit water started seeping out from around the base of the sink onto the glass countertop. Very consistent amount appearing all around the edge.

A few other notes:
- The drain that's installed is definitely a drain with overflow.
- Overflow hole is lined up with the overflow hole on the sink as best as I can manage
- The drain diameter is not the exact width of the drain (drain how is 1,77" but it's very close, and if the issue was space between the drain and the sink hole I'd think that gravity would pull the water down into the vanity cabinet, no?
- Despite the water seeping out from around the base of the sink, no water is coming from under the sink back out through the sink drain hole of the countertop

Any ideas? My concern now is that there's a leak somewhere in the sink itself, but open to other suggestions.

The beveled washer may have been installed UNDER the counter instead of between the sink and the countertop.

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

This is going to seem like a duh moment so apologies, every plumber has done some of these so don’t feel bad.

1.) Your sink drain could be too loose, needs to be tighter to seal correctly on the washer or you could be too tight causing rubber to grab.
Solution: Look into getting some plumbers dope to help this.

2.) You don’t have any or enough silicone or plumbers putty or the rubber washer your sink came with is terrible and made by bad people to frustrate you.
Solution: Remake your seal see if there is adequate material, err on the side of too much you can always clean it up.

3.) In an effort to make a snug seal you pulled down on your tailpiece (that is the drain running to your ptrap) and compressed whatever you used to make the seal on the top or beveled washer on the other side. When you let it go it lifted just slightly and broke your perfect seal.
Solution: Reset your sink, remake your seal check your beveled washer.

4.) You do have a defective part somewhere in the mix. The sink has a micro crack you can’t see and can hardly feel, or your drain threads are imperfect, or the sink has a slight dip in the glaze on the drain. Or on and on and on...
Solution: If you take the sink apart and run a pencil on its side where you think a crack could be you might see a line appear where there is a micro crack. If none of this helps call in the cavalry (I.e. a plumber) and see what the problem is then post it for the rest of us to see.