Figured mine out... it turns out square corners are a symptom of a memory leak.
Dynaheir
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I'm having similar issues. This component is flakey at best.
My issues... the poster is randomly losing its rounded corners. In my case, I'm adding badges and overlays to the internal imagveView.overlayContentView.
To be honest, I've had nothing but trouble with the TVPosterView since I started using it. Fix your stuff apple... provide us with well thought out polished api's and not just pretty devices.