I think it is the RT.

Using Style - _INFUSE.STY (Infuse Bro Country Rock)...

which uses the Bass RT - 4446:Bass, Electric, BroCountryPulsingAB Ev 110

I start an SGU with (key of F) - Bb2/F...F....Bb2/F....F....
(dots are for clarity, not holds)

The Bass plays a Bb on Bb2/F

When I change to Bb/F it does play the F