Please check your PM. Below is the topology I suggested for your 20 DMs. The Inside Orico P10-U2 diagram partly explained why leave one bottom port empty.
Thanks dmsp. After reconfiguring my DMs across the hubs, my rig has been stable for 48 hours. I'm happy.
Just to be clear to everyone, if you fill an Orico hub with 9 DMs, it is critical that you leave the correct port depopulated, as per CruzCoins' and dmsp's diagrams. If you depopulate the wrong port (which I did) you will see stability problems.
Thanks again for the great support!