Could it be that this Amlogic processor is one of the first Amlogic processors to support hardware decoding of VP9 profile 2. And that VP9 is a Google video format used heavily by YouTube.
And thus h.264 and h.265 may be driven by a software library. And that this library may be supplied as part of Google Android TV - Oreo.
And that this library may not like open GOP's where a b-frame references cross GOP boundaries. And if there is a video that demonstrates the problem and this video passes H.264 certification and not work with Amazon Fire OS Cube maybe the Cube H.264 could be decertified.
That would tend to piss off the 1000 pound gorilla.