....all my turrets and spotlights at Sanctuary just vanished. Poof.

No attack, no warning, they're just gone. Power lines connected to thin air where laser turrets and spotlights SHOULD be.

I'm no stranger to Bethesda's games (or the bugs therein), but REALLY?! I've been playing pretty much daily since launch and I'm STILL finding new bugs??

What in the world.

Can you click on the turrets in workshop mode? If you can, maybe storing them and placing them out again will fix the bug.

Did your settlement defense go down?

No, there was nothing to click on!

Ended up replacing everything. Defense had dropped from >160 to like 30 (there WERE a couple turrets left, and the town guards).

Preston probably did some redecorating while you were on a mission

Are you on a PC?

If so, you might want to try disabling Collision and flying down below the floors to see if they sunk into the ground. I've had this happen to me a couple of times with mostly non essential items (NEVER Turrets, and certainly not all of them at once). I was able to retrieve/move/dissemble my stuff from there. I once came home to find my Clinic sunk half way into the floor. I can olnly assume that the Dr. had decided to expand his practice to those Poor Little Mole Ratties

http://www.gamesas.com/topic/1576270-ps4-turrets-disappearing/

This happened to me too. Thankfully only once now. I replaced them and it never happened again. Now it did happen after I built a bunch of turrets in all the other settlements, but hasn't happened again after building more turrets in other settlements.

No, this is what happens when you eat too much Salisbury Steak.

Apparently few days ago, I noticed some of light bulbs in my settlement were gone.

I thought I forgot to made some, so I entered workshop mode and those light bulbs appear...

Nah, Pvt. Garvey mans an artillery piece high atop a wall at The Castle.