If you're replying to this thread, please mention your setup (just the launcher, emunand installed, emunand updated) and how you boot up (holding L or not), cartridge inserted or not.
For me, a lot of the problems seemed to have gone away after updating my emunand to 6.3 and booting up through the GW menu (by holding L).
Holding L long or short doesn't seem to make much difference for me though...
For example:
I turned it on last night, did the keep holding L thing: 3DS hung with white lines.
Turned it off and back on: removed game card and booted up holding L: hanging with white lines.
Turned it off and back on: game card was in, just held L til in the GW menu, then entered emunand: white lines for 3 seconds then emunand loaded (normal for me).
I normally always used the last way of booting up, and it hadn't frozen on me for at least the last 6 times or so that I turned it on.