I always use anti sieze on the boat trailer studs and never had a problem with the losing up. I do use a torque wrench installing.

Learned may years ago:

1- use a torque wrench
2- clean rust off area where wheel rests on drum/rotor because once rust wears off wheel then is loose!
3- not just trailers but all vehicles

THAT was your problem. WD40 is barely a lubricant, it's water based so that didn't help you much at all. They still heated up. You can't use lug nuts to "clean up threads", as it will destroy both the lug nuts and the studs. They may have held, but you weakened the threads on both of them. You need to use a proper thread restoring tool. And lug nuts are expendable items. Any issue that you can't quickly clean up with a thread restorer, pitch the lug nut. It's better to pitch a lug nut than destroy a stud, or even worse.

“BUT ITS JUST A TRAILER!” - me, in a moment of dumbness.

I’ve been very careful about grease, torque settings on the hub, etc, but figured just running them down even with the impact was close enough like your typical garage monkey, but nope.

Many amateur hacks led up to a wheel passing me by on the highway, and I’m very thankful it wasn’t worse. Thanks for all of the input, and hopefully someone else learns from my mistakes.

I'm a retired auto mechanic and have literally installed thousands of wheels using just an impact wrench and never had one come loose or break off the studs (that I know of!).

They didn't replace the old lug nuts did they? There are 2 different types. Conical or cone and radiused or “ball” style . They don't look drastically different however they don't play well with each other at all.

I've also never used a torque wrench for lug nuts and always use anti-seize. Then again, I've had the same Blue Point 1/2" impact for 40 years so we've developed an understanding.

Since they have been working for 5 years, that's probably not the issue.
Yours are probably conical. Couldn't tell for sure from the pic. You can tell by looking at the area of the wheel where the nut seats. Conical is a straight 60 deg taper (like a funnel). The ball type is scooped out so a ball shape would fit and make maximum contact.