This is the top result on google for this issue that the imgur link shows of the array flashing drives on and off. Though this thread was not very helpful for my case I can say that this was caused by me mistakenly running rclone copy to /root instead of /mnt
Basically I filled my USB drive to the max with an rclone process and I saw this flashing. Figured I'd share since this a top google result. Check your USB drive space.