I started noticing this after the April Folders update, but now it is getting to the point where this problem is making the system borderline unusable.
Anyway, here's the gist of the problem: my 3DS's sleep mode is busted. If I put it in Sleep Mode, and leave it there for more than a few minutes (I think five minutes is the max I've managed so far), I can't retrieve my system from the sleep mode. It just won't wake up. It's still on, everything is still functioning. It continues getting StreetPasses, continues getting stuff over SpotPass, drains the battery and dies... but I can't retrieve it from Sleep Mode, and to use it again, I have to long hold the power button, turn it off, and then turn it on again.
The really weird thing is, when the system is in DS/DSi mode (as it was when I was playing Pokemon Black 2, for example), I can literally leave it sleeping for days, and there is no problem; the issue seems to be specific to the 3DS mode.
It's really annoying because you get the most from your 3DS is you don't turn it off, and leave it on to connect with StreetPass and SpotPass; leaving it in the cradle and such, and this completely cripples my system. Hell, playing something like Resident Evil Revelations becomes hard, because I can't just flip the system shut and expect to pick up from where I left off.
Does anyone else's system do this? Any suggestions on how to deal with this?