I'm not a developer but I have the public beta installed (17J5501I) which I think is the same as b2. BBC iPlayer is working fine for me as I was using it earlier to watch Glastonbury. I'm using app version 4.62.0 released 20 June 2019.
As mentioned above, I'm enrolled in the public beta. I've just updated to 17J5515e (i.e B3 equivalent) and have the same iPlayer app as mentioned above. I still haven't experienced any issues with BBC iPlayer.