It's not working for me, perhaps it's an issue in this particular Qt build.

However, in the meantime I recompiled with better CPU-specific optimizations and restarted with gen=-1
and genproclimit=4 in the config, and it now runs with 4 threads. Maybe it was some glitch about detecting 2 actual CPUs vs. 4 (hyper)threads.

It's not really essential though, given GPU miners, hence not listed in my urgent issues