NZBGet : Search

NAS and docker - seems a lot to configure.
As a test I suggest to install nzbget on a Windows PC or Mac and configure SSL there. You don't have to configure news servers or anything else download related.
The certificates from selfsignedcertificate.com should work (with a warning in browser).

Downloading from Usenet requires computational work. High CPU usage is normal when the download speed is high.
What's your download speed?

If you install NZBGet using installation package from nzbget home page, then you don't need to change "UnrarCmd" from its default value "${AppDir}/unrar".

If you install nzbget from some other repository then you probably need to obtain unrar somehow.

You can download nzbget from nzbget download page. It includes everything what's needed including unrar.

Unrar for most platforms is also available from winrar website.

If your nzb-files are properly named you can use %dn in VideoSort to use nzb-name as name for video file.

Add them as separate news-servers.
Optionally you can also use option ServerX.Group for better handling of download errors.

According to the log the download was successful.
The only unusual thing is that the leftovers of par-repair were not deleted (these .1-files).

RPi needs a good power supply unit.
Is this HDD powered via USB from RPi? In that case you need an even better power supply unit.

Is this reproducible with a certain nzb or random?
You don't use an sd-card with nzbget, right? Sd-cards wear off pretty quick.

If you use a custom cypher in nzbget setting try disabling it.
See the topic just below yours.