After update, AME uses all cores for about 1 min then switches to one core only

Since doing the most recent update my AME render times have increased by a factor of 7 to 10.  I took a look at the CPU usage and it's running on all cores to start off but after a minute or so of rendering time it uses only one CPU.

I found some discussion on this topic but it was all from 3+ years ago and it looks like it was never resolved.

Can someone point me to a more recent solution to this problem?

Thanks in advance,

rgames