Recently, the Focusrite no longer locks onto the Kemper as the external S/PDIF clock when you select this option in Focusrite Control.
It now locks, IF you set it to spdif first (with kemper switched off) and then turn on the Kemper. Not ideal at all when producing but at least it locks... However, It still crashes. Bizarre. Even when I unplug the spdif and back in again like you did, that doesn't work. I have to fully shut down the Kemper and go through the steps again in order to get it to lock... but then like i said, it still crashes.
Update from Kemper Support, there is a 30 day return policy starting from when I purchased the first (faulty) Kemper Stage. It does not renew or start again from when I get sent a replacement. So it took a week to identify all the problems, a week for them to send me a returns box, probably a week to reach them and then a week to get the replacement back to me. At which point, if the replacement has any faults I can only exchange for another one, not refund for my money back. So I advise everyone if you have faults, do not take an exchange! Refund it! Buy another one, so your 30 days returns policy starts from scratch. Then if you keep getting problems and want your money back, you can.