Thanks for the image. I can confirm that my Line6 Helix Floor has the same issue. I took the rear panel off to try and see if I could at least reseat the MCU or the cables connecting it. I, too, have to figure this out on my own because there are no stores or techs in my area.
The IO board is a pain to take off, with several screws to remove as well as rings for the 1/4" jacks. Then, you have to disconnect the PSU cable, and one cable leading to the expression pedal. That is the only way you can flip the board into the position shown in the picture. The MCU is on the underside of the IO board, physically connected to it by headers on the bottom of the daughterboard. The cables attached to it are glued at the ends.
I'm on firmware 3.60.0, and I have the same "Updating UI MCU Firmware" freeze issue. I reseated the MCU, reseated the USB2.0 connector, and pressed on the ribbon cables attached to it, to no avail. On Windows, nothing shows up in Device Manager, and 1/3 times that the USB cable is connected I receive a "USB Device Malfunction" message. I tried different USB cables, different computers, too.
Line6 Updater does not recognize the Helix, and the footswitch combinations for Safe Boot Mode, Global Reset, or anything else for that matter, do not work.
I have submitted a ticket with Line6 Support, but am not optimistic they'll have any advice outside of "take it to an authorized reseller/distributor/tech/store, etc." Let's hope they can help in a meaningful way.
