I ran scraped proxies through all the test for 5 times. From 800 working proxies down to 150. I think it's not proxy problem. Every time after the PR checking problem every functions of SB stop working. It can not connect to Internet or something. Even checking proxies will show "problem try again in few seconds". Can not do anything even with direct connection. However if I restart SB everything work fine again.
Okay, might not be proxy prob then. Just mentioned it because since the goog proxy test freaked out some people when it was first rolled out, I believe the default setting has been to have it turned off in the last few versions.
Could be flood protection on your router, or your OS may be un-tweaked/throttling (or killing in this case) net connectivity after a certain amount of "heavy" packet transmission, or something along those lines. There's been some posts around these parts before about similar troubleshooting. Search around a bit, I will too and see if I can find the threads/posts....or maybe another helper has them handy?
EDIT: well, I'd like to get those 20 minutes back...we sure have opened up a tonne of threads about the Box here on bhw, haven't we? I couldn't find the thread I was looking for by someone else who's net connectivity got whacked periodically, but here's a couple general/quasi-brute force things you could try in the app:
Help -> Reset All Settings, or
Help -> Rollback to Previous Version
Or depending on which OS you're on and what type of ISP->PC connection you have, you might look into what I mentioned originally about flood protection, tcp/ip packet management (Win has implemented some pretty kludgy security measures in various versions of their OS'es).
peace - gregs.