There are not many owners with the GSV190 yet. As far as I know, it is now only available on the Toro commercial version of the LB 22271. I also have a 22271, and while it may take several pulls after sitting for a week, it does not have the slow starting of yours.
I also use a stabilizer and synthetic oil. The slow start problem is easy to explain but hard to fix, since I don't know what causes it. The problem is lack of sufficient enrichment to start. Maybe there's an adjustment on the linkage so the choke closes more. What the engine needs is a primer bulb.
One thing you must be certain of with this mower and all 'Insight'-type mowers is that the mulch plug or bag frame is properly situated in the cleats on top of the bag chute box, because there is a magnetic kill switch in the RH cleat that prevents ignition if the attachment is not properly seated. Also you have to keep the area clean so debris does not prevent proper seating.