Plex isn't using all CPU

[TouchASpider]

Server Version#: Windows 1.18.1.1973

I have a Ryzen 3600 PC that doesn’t do much besides run Plex. I get to about 3 transcodes (the server should support more) before the Plex dashboard shows my CPU usage as spiked non-stop. I start getting transcoding and buffering errors from my streams at that point because ‘my server isn’t powerful enough’. This isn’t just the initial spike with a new transcode starts, it remains this way until I reduce to 1-2 transcodes.

While Plex says my CPU is at 100% usage (by Plex) I checked Windows and it claims around 30% is being used (screenshot attached). Why won’t Plex properly consume my CPU? I did double-check the PMS and transcoding processes to make sure they don’t have a specific affinity set.

[TouchASpider]

Illustrating the problem…
Task Manager says lots of CPU % is used.

Plex dashboard agrees:

But the performance tab says lots of CPU is available still (as it should be):

[TouchASpider]

Any ideas? Do other people correctly see more CPU being utilized by PMS on Windows 10?