Probably Bigfoot...
First, I like to look for people having had similar issues before contacting support. That's what they ask to do. That's also what their ambassadors ask to do. So I do it. The topic says "Error 500: A server error has occured". So I read a couple extracts and figured I'd testify to a resembling matter. Now, these policies are a no win: If I contact the support, I'm told to read the threads, if I speak in the threads, I'm told that I'm off topic when the title is THE EXACT ERROR MESSAGE I'M HAVING... Off topic??? No, sorry, that's not off topic.
Also, the forums ARE filled with people complaining about C7 instability (just type z-wave hell C7). It is crazy unstable for some of us. At this point, I cannot believe this is just a device issue. I have tried many things over the past 10 days. Just associating 1 first zwave device after full reset was already filled with problems such as not only generating a ghost device if the device is a bit too far from the hub, but also having to take the time for a cold reboot to get rid of this ghost device, which would not always work on the first attempt (getting thos ridiculous SDK statuses such as "the device is failed but, you know what, we are going to consider that it is not so we won't delete it you bastard" (that's at least the way I started to receive those messages at some point 
). And this happened almost every other device I would associate... And that's really not all. Then, after only 5 or 6 devices, bam! Locked zwave 2 minutes after reboot. Then reset (zwave reset), associate entirely different devices, only zwave plus devices, able to make a couple work for a while then... bam! All nodes dead with no chance of recuperation. Serioulsy?
Now, I have decided to migrate what I intended for this hub back to one of my C5's. No choice, had to finish with this crap, no more time to spend days on it. It all worked immediately, except for one brand new GE wall dimmer that seemed to block the entire network... Took me a little while to figure that one out but, at least, there was a CAUSE that I could find.
When I was attempting to use the C7's new Zwave chip (that is, from 10 days ago until yesterday), I did not own this new GE Zwplus wall dimmer yet, so that could not have been the issue. But, again, I had issues after installing any device on the C7... Zplus devices are generally ok, even if they can make you go through the ghost hassle, they generally pair fine with the C7... But non-plus devices, OMG! It's crazy insane and unstable.
I think I'm having a serious hardware issue on this hub, period. 10 days trying device after device, letting the hub rest, doing everything the doc says, starting over... It never worked. I had hubs for the past 10 years... Never seen such a mess, except with Smartthings, but that was mostly cloud issues.
Again: I have several hubs, 1 C4, 2C5, 1C7. C4 is now decomissioned but it worked well. C5's are working, I have like 60 Z-wave devices on one of them, no problem and, when there's a problem, there's a cause I can find, disabling apps and/or devices and infer the one causing the problem. On the C7, what I OBSERVED was that any device was a fair candidate because the hub's behavior was simply erratic.
Now it just crashed with error 500. WTH?
Just a couple examples of people struggling with C7...
