I'll add that I'm running into this exact same problem when running Migrate DB Pro, another popular plugin written by the excellent folks at Delicious Brains. They are very strict about writing great code. In looking into the nginx logs, I noticed that I was running up against the rate limits, so am glad to find this thread. QROkes, I love Webinoly and thank you for creating and supporting it - I now run it on all of the 5 servers that I manage. It would be nice, though, if there was an easy setting to adjust the rate limit - I don't mind too much editing the nginx conf files, but I'd rather not if I can avoid it. In any case, keep up the great work!
Regards,
Jeff