Attach the monitor on gpu2.
no video out on gpu2
What cable do you use?
Those sapphire have hdmi output and display output.
My trick is use a hdmi to dvi cable adapter.
I plug the hdmi dongle into the sapphire i plug a dvi cable into the dongle and into a dvi monitor this stops the 4mh issue.
Sapphire cards seem to always have black screen no video out issues via the hdmi jack.
I first had this show mining btc with hd 7950 sapphire cards.
Back to rx 470 I have three or four Dvi to hdmi adapter to get past the issues of no video
Which I think causes the 4mh bug