I had already downgraded at this point so I went ahead and tried restoring purchases. Still same behavior. I upgraded back to 5.8.5 and tried Restoring Purchases again. Still same behavior.

To me it sounds like the firmware was not installed correctly. Could you try reinstalling the 5.8.5 firmware using the Direct Updater via USB? The Direct Updater is bundled within H9 Control. You can find it by clicking "Window" -> "Open Eventide Direct Updater" in the menu bar of the Mac version of H9 Control.