Scrubbing timeline looks correct, but preview play does not show speed change

Hello,

I've got a b roll clip on top of part of my video. I've changed the speed to 250%. This is from the Android built in screen capture (not sure about variable frame rates, bit beyond me). The b roll clip played fine before the speed change. I've used clips from this same source in previous video projects and even sped them up without issue. I'm on a Mac.

If I scrub the timeline, it looks perfect. If I play in the preview window, it incorrectly plays at 100% speed until the end of the clip and it starts speeding up. 

I tried closing the project, clearing ALL cached files (via Premiere preferences). But it's still the same. 

I *assume* the preview when scrubbing (which shows what I would expect) is the correct one. But it is very hard to edit without seeing the correct b roll in the preview playback. 

Any advice to fix playback? Many thanks in advance!