Install everything. You can take a backup in My OSMC to a USB stick to avoid too much reconfiguration if it happens again.
Don’t connect the USB drives for a while if you can.
If all is fine, connect one drive at a time. Powered one first if you can.
It will take a bit of time to find the problem but you will find it this way if it’s a hardware issue.
Failing that, we’ll get you a new unit out, no problem.
Sam