Speaking of Common QFN Issues...
The best way to deal with this is to fill the holes with something that will still do a good job of conducting heat away and then plate over the holes.
Barring that, you could put solder mask caps over the holes on the component side shown here. Most manufacturers recommend that the soldermask cap diameter be 100 - 125 um wider than the via to minimize voiding and thermal insulation.
Some people will put soldermask caps on the back side of the board. That may work, but it still tends to be problematic. Solder can still wick down in the vias leading to excess voiding. The via caps can pop open resulting in an open via that sucks solder off of the pad.
Look closely and you might see Paul Lynde in the center via