Ran into the same thing on a panel in a garage that got full afternoon sun. Those wire nuts would loosen up every summer from the heat cycling and I'd get called back for random trouble signals. Switched to crimp sleeves with a good ratcheting crimper and never had a callback on one of those panels again. The trick is you gotta use the right size sleeve for the wire gauge and give it a solid tug after to make sure it's tight. Dave was right, vibration and heat will walk a wire nut loose every time, it's just slow enough that you don't notice until it bites you.

Ha, hold up @kim_ramirez3, checking the rockers is great but it ain't the whole story. A motor can look clean as a whistle up top and still have a rod knock waiting to happen, I've seen it twice now. Honestly the test drive tells you more than the compression numbers do, does it pull hard, does it shift smooth, does it smoke when you get on it. Compression is just one piece and people treat it like the final word. You still gotta drive it and listen to it, that's where the real truth lives.