Hi,
I updated from IOS 13.3.1 to 14.6 on my 1st Gen iPad Pro 12.9 128gb and have the same problem.
After the update everything seemed fine until I opened the file explorer app to access my external usb hard drive. When I clicked the drive name I received an unknown error and it refused to open. The drive switched from its drive name to a “unknown”. Naturally I unplugged the drive and plugged it back in, now whenever I plug in the drive the ipad restarts within 10 seconds and will continue to restart over and over until I unplug the drive.
The external drive works fine if I plug it into a laptop and I confirmed its the exfat or whatever drive file type compatible with IOS; it just appears they broke something in the icloud/file finder that now causes my iPad Pro to reboot endlessly