Just finished my first TV mount installation — a few observations

I had a similar headache when I put up my 65-inch Sony last summer. My Zircon sensor kept giving me "center" readings that were actually just catching the edges of some metal conduit. I ended up with three "mystery holes" before I realized the previous owners had used some weird non-standard spacing in that corner. It’s nerve-wracking when you’re holding a heavy mount and the drill bit just spins into empty space.

I eventually switched to using a high-powered magnet. Sliding that along the wall to find the drywall screws is the only way I trust now. If the magnet sticks in a vertical line, you know the wood is right there. It saved me from making the living room look like Swiss cheese.

I totally get the paranoia about the level, too. I used a four-foot level across the brackets becasue those tiny ones that come in the box are ussually garbage. Getting those lag bolts flush is a real workout if you're doing it by hand. I had to go grab my socket set from the garage because a standard wrench just wasn't cutting it for the final inch.

I gave up on electronic sensors years ago after they kept flagging my plumbing as wood. Now I strictly use a neodymium magnet tool—the StudBuddy is my go-to. It literally sticks to the wall where the drywall screws are, wich is the only way I can trust I’m actually hitting the center of a 2x4. There’s no guessing with the lights or beeping; if the magnet holds, the wood is there.

When I mounted my Samsung Frame last year, the studs were 24 inches apart instead of the usual 16, which meant the mount wouldn't sit where I wanted it. Instead of poking holes or compromising on the location, I cut a piece of 3/4-inch birch plywood and screwed that into the studs first. It gave me a rock-solid surface to bolt the Sanus bracket onto exactly where I needed it. It adds about an inch of depth, but it's way more secure than relying on luck or a sensor that might be picking up a PVC pipe.

Glad it feels solid now, but have you ruled out the possibility that you were just catching a fire block or some horizontal bracing instead of a true stud? If the spacing felt off, that might be why your sensor was acting up. Also, did you check for any electrical lines nearby before you started probing with the nail? Sometimes those false positives are actually shielded cables or conduit running shallow. I'd definitly keep an eye on it for a few days to make sure there's no settling or hairline cracks forming in the plaster around the mount.

While the structural integrity of your installation appears sufficient for the time being, I am curious if you meticulously verified that your pilot hole diameter corresponded precisely to the root diameter of the lag screws, since an undersized bore can frequently cause the timber to bifurcate under the immense pressure exerted by the threads during insertion. I also typically recomend utilizing a depth-stop collar rather than relying on visual estimation, especially when working in older homes where the dimensional lumber might be more prone to brittle failure or where the wall cavity depth could be significantly shallower than what contemporary building standards would lead you to expect.