I've been using the 500x consistently in rehearsals for about six months and had finally felt comfortable enough to leave all of my other effects at home (with the exception of my FLUX:FX iPad app...it is stellar!) As Murphy would have it, it started crapping out on me at the worst time. It seems that the up and down switches (on the left side of the unit with the arrows) started coming to life on their own and scrolling though all of the patches. I didn't notice until I hit the D button; it should have unleashed a thick distortion preset, but instead I had to solo with a funky clean slapback patch...after my embarrassment died away, I was able to laugh along with everyone.
If it were just the one time, no worries, but now it happens at least a few times each set. I admit I am rough with the thing. It is in and out of vans and cars and gets banged up fairly regularly. I've since tried upgrading all of the software and restoring to factory settings, but it didn't change a thing. The only way I could get it to stop cycling (apart from selecting a random patch with the A,B,C or D buttons) was to give the side of the board a knock with my heel. That stops it. I'm assuming it's all hardware.
I've no problem with sending it in for a refurb, but I wanted to see if anyone else has had this issue.
Also, after spending a lot of time tweaking presets, I'd noticed that anything with distortion was feeding back though my powered speaker or any amp I'd try. After frustrating a wonderful sound guy to no end, we cut the drive and volumes on the pedalboard extremely low and used a combination of the amp and the XLR to the house mains to get a decent show volume. After surfing the boards I'd discovered that the patches I'd built had the input sources both set to guitar+aux or guitar+aux and same. Apparently this creates a feedback loop you can't tweak away. Once I switched input 2 to variax or mic, no issues. If this has frustrated anyone else, give it a try.