Hey gang!
Ran into a weird issue when connecting the HD500(X) with a DT50 using the L6 Link. The display would flash the "knob settings screen" and lock-out operation of the knobs and buttons.
Initially, I kind of cured it by reconnecting the link after changing the Setup, Page 1 - AMP/KNOBS DISPLAY to "Momentary: OFF." Then I noticed my HD500 presence knob operation was erratic, but if I used the DT50 presence knob instead, it was fine. Did some more investigating and here's what I discovered, purely through trial and error.
Why it happened and the fix: In Setup, Page 1, (press and hold "View"), I had set the footswitch mode (FS Mode) from "ABCD" to "5-8" so that I could run multiple effects and turn each of them on/off with a dedicated footswitch. My DT50 didn't like that when using the L6 Link. I had to disconnect the L6 Link cable to get the buttons and knobs to respond again. I changed the footswitch mode back to "ABCD", reconnected the L6 Link and everything worked fine, This one took me some time to figure out, so I thought I'd pass it along for anyone else with the same issue.
I let Line 6 know and suggested a software update so that we control freaks can run 8 dedicated footswitches when using the L6 Link. Ha!