NMIs tend to occur with MCA machines because of various hardware weirdness, bus timeouts, and many other non-critical things. Various Pentium machines have had serious problems with the FPU test in bugs.h. Basically, the machine hangs after the HLT test. This occurs, as far as we know, on the Pentium-equipped 85s, 95s, and some PC Servers. The model 80 has a raft of problems that are just too weird and unique to get into here.
Some people have no trouble while others have nothing but problems.
I'd suspect some problems are related to the age of the average 80 and accompanying hardware deterioration, although others are definitely design problems with the hardware. Among the problems include SCSI controller problems, ESDI controller problems, and serious screw-ups in the floppy controller. Oh, and the parallel port is also pretty flaky. There were about 5 or 6 different model 80 motherboards produced to fix various obscure problems. Drivers are required for some MCA memory adapters.