Very hypothetical here, but maybe not unrealistic.

On my current rear wheel I always thought one spoke seemed a little thicker. I got the wheel from my bike shop. I've come to doubt them since the hub is a little off. I thought the wheel was something they had off the shelf, that they got. And that's possible. But they could have built it themselves too. This is the same place that told me my brakes wouldn't work after a repair (after this 32-spoke Mavic wheel in fact) from the bike they originally put together (I think). I went home, fiddled with the brakes, and had it working again in a few minutes.

So if they built the wheel... What if they used one spoke that was thicker than the rest?

Would it be under higher tension?

Maybe that's what took out my rim recently.

Assume that the wheel went out of true a bit for several months. Also assume I had the wheel trued up enough in the fall, it was still fine/trued, but then spoke started blowing out the rim.

What would happen on a wheel if one spoke was thicker than the rest? And the wheel was trued up, but the wheel also got a lot of weight on it from use?

If we're talking hypothetical here, if a wheel with all 15 gauge spokes were to have one of those spokes replaced with a 14 gauge spoke, and the tech doing the job thought he/she were balancing the tension by bringing that spoke to the same audible pitch as it's neighbors when plucked, the thicker spoke would be way over tensioned compared to the others.

I have a set of new-in box Campagnolo Vento CX wheels. Both wheels have a single spoke that's thicker than the rest, and they're also silver instead of black like the others. So it may not be an uncommon practice.

You can use an adjustable wrench as a gauge.
Snug up on a thinner spoke and then see if it slides over a thicker spoke.

I currently have 1 thicker spoke on a wheel I built because of a head failure.
I'll buy a replacement when i make my next spoke order, but I'm not going to worry about it in the mean time.
I'm sure it has a different pitch when plucked, but I don't care.

You really need to focus on the BASICS!

Some wheel manufacturers use different spokes opposite the valve stem to improve the balance.

For a perfectly true rim, all spokes (on the same side) would have equal tension regardless of spoke gauge. A thicker spoke will elongate less at a given tension, but the rim only responds to the tension (the pull force).