Reverse Bulbs On/Off Randomly

[Skeeter McSkeet]

Hey all, noticed that my passenger side reverse bulb was out and I just had changed it a few months ago.  Randomly found out if I shut the tailgate a little harder (not slam it), it will make the reverse light bulb function again if it was previously off.  I can't replicate what is going on to make it go out; but when I unlock the truck and I notice a reverse bulb not on, I'll open and shut the tailgate and it brightens right up.  Only has happened on reverse bulbs in the tail light assembly, mostly passenger side, but I believe it has happened on the driver side a couple times.    

 

It's a 2015 Sierra if needed for reference.  No idea what is going on, it's been doing it for the better part of a year on and off randomly from what I can tell.  I'm the original owner. I did slowly back into a tree in the woods one night with the tailgate down (going around 3-5 mph).  Unfortunately I had to have entire tailgate replaced minus the guts a couple years ago, as it dented the top of it pretty good.  The impact was closer to the passenger side,  I'm wondering if this is linked to the bulb problem in any way?