My pc is strange

[Justsomeplayer]

So I recently got a ryzen 5 3600 and 3070 so first thing I tested Minecraft(1.18.2) at first it was running 300 fps on 16 chunks and max setting which is normal for the spec then later when I load it up again it give a max of 130 but mostly 70 fps to 5 fps
which is really weird I didn’t make any changes in the setting

anyone know what happen here?

spec
ryzen 5 3600
3070
16gb dual channel 3200mhz
b550m phantom gaming 4

all drivers are updated