Check
Not 'always' penetrating
If you've prepped and applied it properly with the correct mix and consistency and in date gear, I'd be surprised, (you can test for this). You do have holes and pores still there visible so it could be coming through those.
Moisture in the air - in the room can gravitate to the coldest spot, and condensate and eventually turn to this.
I'd brush off the white, hit it with at least another, making sure it's at 90⁰ the the last coat applied.