I did more testing on this, and the last kernel I tested that would start all four CPUs was kernel-default 5.9.14-1.1.gc648a46 from obs://build.opensuse.org/home:tiwai. It failed to start three of the four cpus on the kernels from 5.10 and 5.11 when running Tumbleweed snapshot 20210328. It still runs and boots all the way to the graphical environment, however performance is greatly diminished.