I'm pretty sure the only time they give out loss forgiven is when the issues are on their end. Mainly because there is no way of accurately telling if you just have bad connection or if you are intentionally disabling your internet to try to get loss forgiven (not that you are, but if it worked that way you know people would abuse it).Plus usually when they are having issues they have a warning message or even disable ranked queues.
On the other hand, if it is on their end and they didnt have any warnings up and you lost because of it; then ya I do think they should just not make the game count as part of the series. I kind of also wish they'd give loss forgiven if a teammate is gone the entire game. Last season when I made it to silver 1, I lost my next 4 games and got demoted right away and two of the games were 4v5 the entire time.