I had the same problem. After some troubleshooting, this is what worked for me after the 2.21 update failed and bricked my Helix which was still at 1.0.2.
LIne6 updater showed the version of my Helix as 2.21 in the hardware list, but the update failed about 20% in. After several attempts from my laptop, I tried applying the update again on a desktop computer with varying USB ports with no luck. A factory reset boot pressing 9 + 10 did nothing. I tried applying the next incremental update of 1.06.5. Still no luck.
When I troubleshoot, I normally only try one variance at a time. However, I was finally able to get the update to take. I'm not sure if step 1 or 2 actually fixed it, but this is what I did thanks to this post.
1. I booted the Helix holding down 6 + 12. This didn't seem very promising because all I got was a completely blank screen.
2. I then tried applying the very first 2.0 update. The screen then started to show a lot of pixel noise looking like a shattered phone screen. However, the update worked! It rebooted and was back to life.
3. I performed the factory reset booting up with 9 + 10.
4. I repeated steps 2 + 3 using 2.21 with success.
I haven't had time to actually play through the unit yet after being updated, but at least everything seems fine now.
