You are my heros gr5 and CarloK!
Bricked my UM3 caused by an faulty patch by Bondtech for Bondtech QR feeder.
Um3 looped at startup and never finished booting.
File recovery-5.2.1120190503.img provided by CarloK brougt my UM3 back to life.
After Wifi-Setup another update was done by Air.
Everything fine now, also afterwards putty patch for Bondtech QR extruder Steps and speed.