So what’s been revealed in this post seems germane to this discussion:
Boards are still random (or pseudo-random technically), they just use a seed to generate them. This seed is redownloaded on a set interval to your device which generates the random board. The time on each seed is 20 minutes per some previous research done by @Gryphonknight and @Kerridoc. What is the issue here is that the Beta account on a device and the Live account on a device share the same RNG Seed.
That seems to indicate that it’s very possible that they are not, shall we say, extremely diligent about making sure that each pull, or even subsequent pulls at the various portals does not have a different seed, making it possible that some accounts would be subject to a bias toward (and away) from certain heroes.