Drobo 2nd Gen in reboot loop, but will complete data preservation

I have an old Drobo 2nd Generation. I recently added a fourth drive to it. Now, what happens is that the drobo will go into a reboot loop. It will come on, all the lights will be red, then it reboots.

Now, if I take the fourth drive out, power it on, then put the fourth drive back in, it will power on successfully, and I can access data for about 17 hours while it performs a data preservation/validation step. Then, it may or may not stay powered on for a while. Then, it goes into a reboot loop, again.

My question is - is this the Drobo just failing? Or, perhaps the fourth drive is bad?

I had a similar issue and replaced the power brick and that seemed to fix the issue. Another problem arose, however (the Drobo) wouldn’t stay powered and would go to sleep mode. I finally switched USB ports on my port replicator (Dell) - I had done some rearranging - and then wah-lah - it worked just fine.