Divine Sense (Paladin) triggers combat (should not)

Nuance : it does not trigger combat if you have no line of sight when you use it. 

It does not seem to break stealth as such. 

I will test it some more and report back. 

Did a few tests with a quicksave just near enemies. 

I can confirm that : 

• if I have a line of sight and range for Divine Sense, using it triggers Combat automatically ;
• I remain in stealth/Cautious mode and succeed the Stealth check, but still triggers combat automatically. 

Theory : the visual animation of Divine Sense seems or looks like it triggers a form of detection (though I remain stealthed) and/or is considered a combat action. 

Suggestion : it really should not, in my opinion. 

By the same token, if you use hunters mark while in stealth, it starts combat and doesn't allow you to attack with that character on the surprise round. However if you attack to start combat, you can then use your hunters mark bonus action. However if you already have hunters mark active, you can move it to a new enemy without starting combat and then attack, and then move your hunters mark as a bonus action.

I'm not sure if this all follows with 5e rules or not.

In my reading, re-applying the Hunter's Mark (when it was cast during a previous fight) could/should be silent, so I like the implementation here. 

But losing your Action on the surprise round for casting a Bonus Action spell seems like a bug for the reason you explain...

EDIT : I tested it and I also confirm that the Bonus Action Hunter's Mark when surprising enemies blocks out the Action during that same surprise round.