Using TipJarViewController in an iMessage app

I have inserted TJVC into an messages extension containing stickers, idea being to tap on the tip jar "sticker" (which is actually a button, not a sticker) and go to the tip jar instead of choosing a sticker (which is what happens when you tap on the other, actual, stickers).

I almost have it working, can open the tip jar page, initially in compact mode, and then can swipe up for expanded mode. However, when I swipe down to return to compact mode, view is then blank. I can return to expanded view and the full page screen still shows the tip jar, but the compact view only appears the first time.

Any ideas why this is the case? I am pretty new to iOS, sorry if this is a poor question.

Start with TipJarViewController as it is embedded in the iMessage messages extension, then reproduce the transition from compact mode to expanded mode and back. Investigate why the compact view is blank after swiping down; done means the tip jar remains visible when returning to compact mode.