Added a RTX3050 for hardware accelleration, still have stutters

Hi.

I run Plex in a container in Unraid. Initially I had a GTX 980 in the server.

So I set up the container to use HW acceleration. So when I movie plays, I get this little Plex icon in the GPU Monitor:
 

But there was stutters and buffering, and the CPU goes to 100% on all 4 cores.

This, and the fact that GTX980 doesn't support all HEVC types and no AV1 at all, led me to buy a RTX3050

But the results are the same. I still have stuttering and buffer pauses. And CPU goes to nearly 100% on all 4 cores

But the GPU monitor shows that Plex is an active app.

In docker, it looks like this:
 

I have also set the Extra Parameter: --runtime=nvidia in Advanced Options

Is it simply my hardware that isn't good enough?

It is a I7-7700k, and the server has 64GB memory:

What am I missing here?

Thanks