Post processing not showing in Play mode (LWRP) + bad editor performance

I've started a VR project using the Lightweight render pipeline VR template, and tracking and controls are working fine. I have two issues though:

1) The included Post processing stack doesn't show while I'm in Play mode. What is the reason for this?

2) In the editor / play mode, the game is very jittery, and the left eye flickers about once a second. When I make a build, it's buttery smooth. I assume there is some editor overhead, but is there something that can be disabled to make it smoother in the editor, so I don't have to build every time I want to test, to avoid getting sick?

I'm using Unity 2018.2.6f1 with Steam VR on a MacBook Pro, and an eGPU (sonnet) with an RX570 card and an HTC Vive.

Thank you for any tips!

EDIT: Hmm, when I started a new project, the Post processing effects work (not Vignette though?), so I might have screwed something up. Where should I look? But the jittering is more intensive, and the left eye is jittering so bad I can't watch it.