Not a direct answer, but it might help.
I also have this problem in two zenfone2's, plus slow charging/no charging/overheating/fast battery drain.
I Managed to fix the one that almost never turned on (2GB ram) by replacing the USB power board at the bottom in of the phone, now its working perfectly!
The other one which has the same problems but turns on(3GB ram). The board replacement did nothing to it.
Since the speaker, vibrator, sim, charging are all on that lower board I expect the problem to be either from the lower USB board, or the single large ribbon cable connecting the upper and lower boards and having all the card slots on it.
The lower board is very easy to replace and it's cheap, 5$ or less on eBay. But I can't find the ribbon cable, except for ones that are pre attached to the battery, and those are expensive!
I will test replacing the lower board again today, if there is a change I will post it here. If not don't wait for a reply.
If you happened to fix it, or tried something with it, let me know maybe we could figure it out.
I hope this helped.