Absolutely, this is a bug and it's actually being fixed in the development version today.
But until the next release, as a workaround, you can add the code I suggested
Unprotect[$ProcessorCount];
$ProcessorCount = 4;
to your kernel init.m
file, so it will be evaluated whenever the kernel starts up. To find the location, try
In[1]:= FindFile["init.m"]
Out[1]= /home/pi/.WolframEngine/Kernel/init.m