@jussi_laako sorry for my annoying report again. But this time this is really a big good news! After I tuned my MSI Z690-A Pro motherboard (set OC 5100MHz / under volt 1.3V / DDR5 XMP1 on), 48 family to DSD1024x48 using AMSDM7EC 512+fs finally works!
I think the stuttering once per minute was caused by “uneven” CPU frequency (i.e. motherboard BIOS default was turbo boost mode. Each core had their own freq and also had freq spike). The previous screenshot the CPU loading was not that high for 48 family upsampling so I thought it could be solved by tuning the hardware. After did some research and experiments, it succeeded. One of the benefit after tuning is the CPU temperature looks better. All reasonably controlled between 70~80deg C.