We have been having issues with the FireTV app crashing during playback.
I turned on the debug info overlay today and reproduced the issue, and found the crash occurs when the cache fills up.
When I started streaming the cache number starts at 0 and increases as I would guess the past part of the stream is cached for rewinding. There is a Max value next to this of 400-500 MB (on last attempt it said 486, now starting a new stream it says 538).
Once the cache value counts up to this max, the stream crashes back to the guide.
This is a stream from a remote Channels DVR server, if that matters. This is consistent on multiple FireTV sticks.