As far as i can tell, its a problem of latest kernel 6.8.9-arch1-1
If I switch to LTS kernel, in 8/8 tests the mouse always works.
I looked into the boot-log and tried to compare them with my limited knowledge
As far as i can tell, with LTS these two lines initialize the touchpad:
Mai 05 09:35:57 host kernel: hid-generic 0018:093A:0274.0001: input,hidraw0: I2C HID v1.00 Mouse [PIXA3854:00 093A:0274] on i2c-PIXA3854:00
Mai 05 09:35:57 host kernel: hid-generic 0018:32AC:001B.0002: hidraw1: I2C HID v1.00 Device [FRMW0003:00 32AC:001B] on i2c-FRMW0003:00
but around that timeframe with the latest kernel, there are no error messages indicating that it coult not initialize the touchpad…
EDIT: if someone want to take a look at the boot log i can provide that. maybe u guys can figure out more with it