The segment that is the problem is on a Westjet Link Saab 340, just never seen this before.
It looks like WestJet proactively block all of Row 2 (the first row) on the Saabs, leaving only Row 3 available for Premium advance seat selection.
I have no idea how full the Premium seats usually are on the Saabs, but blocking half of them could mean that this is a regular issue for Saab Premium passengers.