G-Raid Ejects one daily, during the night

I store my photographs on a 6TB G-Raid (2x3TB drives) Thunderbolt 2 which is backed up nightly using Super Duper to another 4TB G-drive with USB. Every morning i get a notice that the G-Raid has improperly ejected. I can only get it to remount if I restart buy computer. Then the cycle repeats again the next night. I have changed the power supply and the Thunderbolt connection but pattern stays the same.

That’s really weird, I’ve never experienced that nor never heard of that