Setting Affinity to only 1 CPU core

I ran into some major lagging issues out of nowhere (yeah I know right?) And while SU was Not Responding… I went into the task manager and selected SU and set the affinity to only 1 core, instantaneously SU responded.

Thinking this might be a fluke, I ticked the three remaining boxes and SU Bogged down again.

I’m running an i5 2500 (not k, XMP @ 4200mHz (peak) ) with a Asus gtx 560ti

Is this normal?

See this post I made a while ago. Still holds true.