I had the same problem. Did some research and I found deleting your history and cookies in your browser sometimes solves the problem. Worked for me! No more of the 502 bad gateway!
A great rumor would be that the NSA is blocking Internet Service Providers browsing traffic until they submit to releasing all browsing data to advertising agencies. Sounds ludicrous, so it might be true.
And ..... here we go again. (and yes I cleaned my cache)
Thinking maybe ABZ needs to address some issues - maybe do a little upgrading. Perhaps a higher volume of traffic triggers some of this.