Frame drops and CPU usage spiking to 100%

Hello! For probably the past ~2 weeks or so, I've been having issues with the game's framerate dropping from a locked 60 to 30 (and sometimes below). I've done all the expected monitoring and in-game settings adjustment (and found nothing to change in the case of the latter). All AMD software extra features are disabled, and both GPU and CPU temps are completely normal. All components in the PC are around 8 years old, sans GPU and PSU.

(Relevant) System specs -

• Motherboard - GA-B150M-D3H (rev. 1.0)
  
• GPU - Sapphire RX 590
  
• 16GB RAM
  
• Intel i7-6700 @ 3.4GHz

For a bit more detail, when in any kind of activity, every ~5-10 minutes, the framerate will drop from 60 to 30, and CPU usage will spike to 100% from around ~50-60% and then immediately drop back down. This does not appear to occur in social zones or orbit, nor does it seem dependent upon general game intensity (enemy count, particle effects, etc.). This typically lasts for only a second or two, though it does seem to get slightly more frequent and intense the longer the game has been running. GPU is completely fine and performing how I would expect. I've never had issues with this game's performance before, and am wondering if anyone else has had this particular issue. It's not debilitating or anything, but is concerning enough to the point where I'm wondering if this is a hardware issue even though the CPU is otherwise fine doing literally anything else, and has never had issues with D2 in the past 4 1/2 years I've been playing it.

Thanks for any help you can provide!