Was kind of away of the tech stuff and didn’t realized intel did something to the hyper threading as we know it.Just to make sure, there is no hyper threading option turned off in the motherboard bios or replaced with newer tech that you can change back there in the settings.
Just googled to see where this started and saw some news from 2017 when the sky lake and kaby lake cpus were coming out having hyper threading broken.Yours is way newer and problems should be ironed out, but maybe a microcode update or a third party app that will force it to work better? Is this on windows 10?
Another thing that comes to mind is that when you finished rendering a scene>open the swarm window>settings>ShowDeveloperMenu> and change that to True.
Now in the Developers Settings tab that will show up>LocalJobsDefaultProcessorCount>try to type in the number of processors.
In mine actually shows automatically the number 32 which are my threads.How many does your udk detects by default?