Why - I assume that the stick is based on Android and Android had implemented no API to automatically change the refresh rate before 5.0.
What makes the stick now and why it jerky? One can say the stick that he should either work in 1080 / 720p at 50 or 60 Hz or to automatically detect this. However, the automatic detection is compared to a genuine recognition of frame rate in the source material only a function discovers that which refresh rates of TV angschlossene can and then decide for. Normally, the higher refresh rate (useful or not).
The problem arises because of Amazon 24p to 50 / 60p has everything on offer. ie at a fixed setting to 60p the stick trying to play both 24p and 50p content. Depending on the frame rate in the content and the frame rate used in the output therefore occur partly. Strong, intermittent stuttering, which, however, differ significantly from the "normal" pull-down judder.
I am therefore not even sure if the stick ever tried a pull-down, and not just try to play and then swallowed the missing frames simply without optimal algorithm or doubled etc.
Bottom Line -> if the connected TV device does not have a reverse telecine Engine (calculated from a pull-down image the Framerate out and gives this also correct from), then jerky picture depending on content used more or less ,
And until that's not gefixed, the stick goes back ... unfortunately, a Big Fail!