First timer bought a house with a pool that looks great, but..

[WoodenNickel]

Wellllll.... that explains the flow not being detected.
I pulled the SWG and the missing piece wasn't lodged in there, so I'm assuming it worked it's way backwards to the filter somehow when the pump shut off? I'll be doing a deep filter clean in a day or two and we'll see..

SWG is generating again.. so one problem solved

 

[WoodenNickel]

I see the filter pressure is up, might need cleaning.

It appears you were entirely correct, thanks for the recommendation! PSI is now happier at 15