I have been searching on this site, and it seems the experts here conclude that it is not possible for air bubbles to originate on the "pressure" side of the pump, which would include the filter and spider valve.
I submit my symptoms/diagnostic tests to you:
In "Filter" mode, air bubbles can be heard running through the filter (no bubbles in pump basket, indicating no suction side issues)
In "Recirculate" mode, air in the system from turning the multiport valve quickly dissipates and quiet operation returns.
From this, I surmise the water passing through the multiport valve is some how sucking air in through a leak.
Thought I'd pose this here, as several threads seem to categorically rule out air bubbles being created at the filter.
(Since it is under pressure, and not suction.)
Also, to lube or not to lube the spider gasket? found some pretty good sounding advice here, which suggests no lube on the spider: