Wondering if this issue has been resolved.
I'm on the cusp of buying an H9000 and intended to create an aggregate with 3 Apollo x8p.
We don't see this issue too frequently, but if it does happen it's a pretty simple fix of just re-selecting the devices in the aggregate device in the correct order.
I have never run into this issue personally using the H9k with multiple aggregate device setups and different computers with different OS. I just tried reproducing the issue on High Sierra using an aggregate device with an Apollo 8p and H9k and the aggregate settings were intact after restarting the computer.