There is a little weirdness on the iMac connection screen, when you connect a second H9 device the PIN input screen seems to default to the PIN of the device that was connected previously. When you overtype the correct PIN, the display in the text entry box on the Mac looks like both numbers are present in the same box, almost as if you wrote the numbers over the top of each other on a piece of paper. Inside that box I've tried select all, backspace and carefully keying the correct pin for the device but it still gives the weird overwrite look and will still not connect.

This sounds strange. Did you connect to your H9s in the application on your Mac?

I do know some users have Bluetooth issues on Macs but I've never seen that overlapped PIN window. Could you take a screenshot of that connection window?