Synology has apparently resistant problems with the on / off switch, across their product line. From three different devices (DS212 +, DS414, DS415 +) have two this problem. The problem is that the stroke (actuating travel) of the on / off switch is extremely short, felt 1-2 tenths (!) Mm, so that a light touch would be sufficient to actuate the button. When DS414 a clear tactile pressure point was available.
Why do I mention this? When DS212 + I had the problem that the device simply shut went spontaneously. After I had studied there, I was able to prove through log records that it was attributable to an operation of the on / off switch - just had at the time no one to each button is pressed!
If you are looking for the problem on the Internet you will notice that there are quite often happens.
I'm not going to replace the device first, but watching the problem initially.