Exactly the same here. Blackmagic will not support the issue. Wish I could get my money back. I was on a PC and was talked into going with Blackmagic. No stream, No support, No way I recommend Blackmagic.
Any word on a solution yet? I am having the same problem. It was blamed on my apple then the modem but all have been switched out and like you my stream becomes unstable with data rates fluctuating all over the board until it restarts the stream. This is the second Blackmagic device that has not worked as advertised. I will not buy another.