ISSUE SOLVED! Hi folks, I had the same issue after upgrading my 11" iPad Pro (2nd Gen.) from iPadOS 14.8 to 15.0.2. Re-installing the OK in DFU mode did not help. I restored my iCloud backup on another iPad running iPadOS 14.8 to get back to work as soon as possible and left my bricked iPad alone for a couple of days. Today, I used DFU mode once again to install iPadOS 15.1 on the device. Afterwards, I was greeted with a white screen stating that it was trying to restore my data. I honestly did not expect anything good from this, but after a couple of minutes my beloved lock screen showed up and I was actually able to log in again without ending up in a respring loop! The iPad ran a bit slow and several apps refused to launch, but after a quick reboot everything was back to normal. Well, except my home screens which have been totally messed up by a couple of automatically set-up widgets... tl;dr: iPadOS 15.1 seems to fix this issue. If you have not reset your "bricked" device yet, you may have a very good chance to get it back to normal by installing 15.1 in DFU mode.