astro stacking excrucaiting slow

[Vega509]

good day to all!

I'm a new user and have been following James Ritson's astro sacking tutorial. I am finding that affinity does the 1st 5th of the stacking quite quickly utilizing 100% of the cpu then goes into slow motion for the remainder of the process using between 8 and 14% of the cpu.

I have 190, 20mb subs, 25 darks, 25 flats, and 25 dark flats in the files selection. I'm working on a 12the gen i7 with 64gb ram and an M.2 drive. the total time for the stack to finish was 3hours 21minutes. siril stacks the same data in under 4 minutes on the same pc, DSS in 16 minutes.

I have allocated 48gb of ram to affinity. there is 457gb of free disk space. I've been through the tutorial several time, and these forums looking for what I have missed in the settings, or am doing wrong without any luck.

anyone have any thoughts on what I've missed?

thanks in advance