I've had a few games (like Dangerous Dungeon) where I'd be playing for a few days, make a lot of progress, then after a few days of not playing it, my save data will be gone and I'll be at the beginning as though I'd never played. Oddly, it remembers that I completed certain quests. This has happened for a few games, any ideas on how I could stop that or retrieve my data?
If you're talking about AG quests, those are saved on our servers. So there's no 'forgetting' that you've completed a quests. Once it's awarded, you could delete all of your data and the quest would still be there.
So now the question is where your game information is saved. For Dangerous Adventures (I'm guessing that's what you meant, as there's no game here called Dangerous Dungeon) it looks like your save info is saved on your computer. So things like clearing the cache or browsing history can delete your save files. I can't say for sure that's what's going on, but that is often the issue when it comes to losing local save data.
One thing to check is whether there's something set up to 'clean up' the browsing history every few days. That would be something you would either want to disable or just play on another browser. For example, with Firefox, you can tell it to delete history that's more than, say 3 days old. So if you don't play the games for 3 days, it'll delete that data. Chrome and other browsers can do the same thing. That's my best guess as to what's going on here.