I've been continously upgrading a couple months behind new releases on commercial projects since 2015. I've upgraded about 17 times so far. Unreal's update story is light years ahead of Unity's half-hearted "automated" mess.
Worse bug I had was back in 2016 when an upgrade lost reset the scale on weighted bones to 0.
Unity often feels like rolling the dice with upgrades, basic things can break from version to version, but I've done many Unity upgrades with no or minimal issues, and seen extremely painful Unreal upgrades
In my mind, the big win from having the Unreal source code is understandability. But also, in contrast to Unity, if you should for some reason need to—say a critical bug that’s stopping your game from shipping at the last hour—you at least have the option.
How about this... stick to small changes, freeze your engine upstream version, or hate your life: pick one? ;)