Why does my Xperia Miro consistently miss the time of the alarms I set?

I’m using my cell phone as an alarm clock and for a while everything was working fine. Now, for some reason, the alarm overshoots the time I set of an arbitrary amount of time.

Generally it either suddenly starts going off the moment I wake it, assuming it’s after the chosen time (Say i’ve set it for 7:00, I check the time at 7:10, it starts going off, I check it at 6:55, it doesn’t, then it does at the right time, usually).

Other times, namely when I don’t wake up around the right time, it overshoots up to 40 minutes (so far that’s the worst it’s ever been late).

I’ve tried clearing the clock’s cache and data, I haven’t reset the phone yet, and I’d rather not.

I suspect it might have something to do with the energy conservation mode for the phone, that could dilate the intervals at which the time is checked to save on cpu usage, but if that is the case that’s absolutely insane, so I hope that’s not the case.

I have cheked and the alarm is set to go off regardless of the mode, and google does nothing.