Many of us have been caught in this situation. It's unfortunate, but there's no way to prove it was a site issue (if in fact it was, because sometimes it can be your connection that's the problem for a short moment). When there are obvious site issues, they do acknowledge it and penalties are waived. That said, if you do get a penalties, the first few for leaving aren't really that harsh - you can still do everything on the site you normally do, and if you keep playing and don't have any more disconnections, you'll recover pretty quickly (in fact, given that was your second recent expulsion penalty, and you've already recovered about 3/4 of your first one, you're well on your way to doing that).
(Note, I have no association with admin of BGA, I'm just a user like you, who also like you, posted at one point asking for my first penalty, which didn't seem like it was my fault, to be waived - it wasn't, I've had other penalties since, and it's just not worth worrying about. Just keep playing.)