I have the same problem. Using HELIX version 1.06.5
Ref; :Updating UI MCU Firmware, please wait do not power off the device"
I tried the following;
Download and install Line 6 Updater if you have already. (version 1.28)
Also download the Helix Flash Memory for 3.15 (version 3.71.0)
Hold switches 6 & 12 when powering up Helix to get into safe boot mode. (Still looping with :-7:-7:-7 on the top Display in red)
Run Line 6 Updater, if it connects to your Helix, used Offline Model and install the Flash Memory file you downloaded in step 2.
I also try to use Line 6 Central (version 1.01) without success. The softwares (Central and Line 6 updater) don't see the Helix. I also try to boot in safe mode (Switch 6 & 12) on power-up without success.
See added info beside 1. 2. 3. above...
I am using iMac with Sonoma 14.2.1
Any other idea ?