ends up the clutch pedal switch was disengaged (retracted), telling the ECU that the clutch pedal was depressed when it was not. I guess the tech must have adjusted the switch for some reason the other day while adjusting my clutch pedal and may have forgotten to readjust
per the Bentley manual, the function of the Clutch Pedal Position switch (aka Clutch Vacuum Vent Valve Switch):
This signal is used to avoid RPM over-oscillation and load change impacts when changing gears and is also used for the cruise control system.
This would explain the driveability issues I had...the ECU thought the clutch was disengaged all the time while i was driving around (hence the "17947 - Clutch Pedal Switch (F36): Implausible Signal" DTC)
pre-adjustment: the switch is disengaged in this pic (on the left...the right is the brake switch). this is with the clutch pedal fully out
measuring block 066: It should say "1000" in the 2nd field from the left since my clutch is fully engaged (pedal out), but says "1100" since the pedal switch is not engaged. Note the field name is erroneously labeled "Brake Position"
post-adjustment: the switch is now fully engaged (as it should be) when the pedal is out
measuring block 066 properly reports the clutch is engaged/pedal up