I haven't been using a VPN, no, and given my setup I think it's unlikely to be a broadband issue. I would try the offline version but it seems like more trouble than it is worth.
I do hope you're able to find whatever the issue might be.
Just a quick heads up, if you were using a controller at the time you had these issues, the most recent patch may have fixed the issue. Given how fiddly the web controller API can be, it would explain why the issue only happened sometimes. If not, then I'll keep my eyes open for more potential causes.