Loosing notification vibration

Not sure if I understand correctly. Is it just the vibration that you are losing while going on to receive the notifications on the screen, or are the notifications missing altogehter?

In the second case, have a look at the thread Notifications for some tips.

The first is correct, the notification still appears on the screen of the watch but no vibration to indicate that a message or similar has arrived.

cheers 

And does the vibration still work for other types of alarms? Or does it work when you turn on the option of vibrating on button presses? If not, then it looks like a hardware failure, and you may need to contact the retailer or Garmin's Customer Support, and send them the device for repair or exchange.

I’ll have to test it, cheers 

... BTW, another possibility is that there were no vibratios because the DND (Do Not Disturb) was on - for example it is (by default) activated during the sleep hours, so do not expect any audible or vibrating notifications during the DND time.

... and (on some watches) there is also the option to suppress audible/vibrating notifications during Activities, so take that in account too.

So the vibrate still works for alarm and timer etc when the notification vibration ceases. 

Can confirm that DND not activated, this sets by default between 23:00 and 06:00. Can confirm that DND is set to off when loss of vibration occurs. Happened this morning at around 10:00am when I first noticed it but vibrations were being received prior to this. Can confirm no “activities” were in progress either.

In that case, try asking on the Forerunner 935 forum, to see whether it is a common or a known problem with that model. If not, contact the Customer Support.