Welcome back! I hope you have a blast with the new content! 
I didn't start having that error until yesterday, maybe the day before. I was the host in a private solo match one of the times and got kicked out on Zone 4 without so much as a by-your-leave without my gold or my xp, quit in disgust, and noticed the xp was 'restored' after I relogged an hour or two later. The second time, I don't think I was hosting (I try not to because, as I understand it from others, it makes eating the ham back at camp seem like a better idea by the minute) but it actually didn't drop me from the lobby either? Because when I hopped right back into MP, I got ported into the same lobby and right into a gip (except it was the same match, we just had to replay zones 3-5) and the guy who had been 'connecting' for the whole match was there, but no one else. The UI was a mess, but I got my xp! XD