CPU capacity utilisation only at 10-20% during rendering

Hi All,

It's taking a very long time (> 7 hrs) rendering for export a 30 min clip shot in 4k , edited on a 4k timeline and exporting to Full HD.

A check on the CPU utilisation showed the utilisation is less than 20%!

All my source files, program files and saved files are on the same SSD Drive.

This is a new i7-8700k, 32 GB RAM PC.

Previously, I don't have issues with 2.7k footages edited on both 4k and 1080 timeline and exporting to Full HD.

When exporting in those instances, CPU utilisation hits 100%.

However, I'm experiencing this very low CPU utilisation on 4k footages on 4k timeline and exporting to Full HD.

Has anyone experience this as well?

Is there a bug in Premiere Elements 2018 and are there any work arounds?

Many thanks in advance.