This is typical behaviour for plugins with denormal problems, but since you’re only using a single powercore plugin then denormals should not be the problem.
and it is new to 1.98
You mean 1.98 and not 1.99?
I have my doubts that it is something I changed in 1.98 that’s causing this. Please verify this by reinstalling version 1.97, load exactly the same project and check if the CPU problems are gone.
Also, try to disable the “Enable plugin multiprocessing” option in Preferences and see if this has an effect.