"Lock Screen of Coma"
First off, I apologize for not having reported this much sooner, as it has been an issue I have known about for a month. I think subconsciously I didn't want to have to type the whole thing up on the bug report site on my phone, and I forgot I could report it on the forums.
OS: Android 5.01
Device: LG Sunset
I'm not sure what is causing it, though it seems to happen most frequently after returning to the map screen from a battle. It has also happened after gathering, and on one or two occasions without any triggering event that I can think of. The phone will briefly display the lock screen and then go to a black screen (with the screen still on). Holding down the power button and waiting at the power options menu for a few seconds usually causes the game to pop back up, underneath, and tapping on the screen after bringing the game back up jumps to the lock screen again (without the black screen). Once it happens, it occurs much more frequently until the app is closed.
If I had to make a guess as to what is going on, I would assume the OS is somehow assuming the phone to be idle, which is bringing up the lock screen, though it doesn't quite explain the increased frequency of the occurrence after the first one.
I'm not entirely sure if the game has gotten an update, but now I am less certain about the "idle time" theory. I decided to check into the game again today and was given the "New version available" note, though after checking the app store when I had wi-fi available, no such update was shown. This time, the game went straight to the black screen immediately after the map loaded (less than even a minute after starting up the app).
I'm starting to wonder if the issue is related moreso to hardware requirements than anything else.
The "new version available" notice is a known issue.
However, this lag/black screen thing is new.
Hopefully you'll get a fix soon.