I have several machines on which I make installation tests from time to time: a Lenovo Ideapad 120S (2017), an Intel NUC6CAYH (2016) and a Dell R610 (2010-2012).
The NUC6 is interesting because it supports both UEFI and legacy boot at the same time. Some years ago, I had installed Void Linux on it and it worked fine. At some point, I reinstalled it using a more recent Void ISO and it failed. With further testing, I realized that whichever OS I tried to install failed when both UEFI and legacy boot were enabled.
However, with just UEFI enabled, I could install any Linux distribution or FreeBSD, but neither NetBSD, nor OpenBSD (nor OpenIndiana and Tribblix, by the way). In legacy boot mode, I could install anything.
The R610 supports either UEFI or legacy boot, but not both modes simultaneously. However, the result was the same: Linux or FreeBSD could be installed in UEFI mode, but neither NetBSD, nor OpenBSD.
I have updated the NUC6 and the R610 firmware to their latest available versions but it made no difference.
I have recently tested NetBSD 9.99.75 on the same machines and installation in UEFI mode succeeded.
I have also tested installations under QEMU with either UEFI or legacy BIOS with identical results, so it is very easy to reproduce these issues if needed.
I have no clue as to why some OS boot on some machines and not on others while other OS boot on any machine. However, solutions exist and get implemented, and that's good. 🙂