Normaly i would blame AMD cpu as it is fairly common that it don't work well with new game releases, most of the time buggs happen with amd chips thats why i avoid them as i get extremely frustrated if shit like this is happening. BUT
I've noticed first day of release it was crashing every 30 minutes, after that fix game was working perfectly fine, then just yesterday it started stuttering (altho verry rare for me) i've noticed that it stutters whenever enemies spawns not always but sometimes. I'm pretty sure its a bug on ubisoft side and it will probably get fixed.
i7 9700k
GTX 1080ti
16gb 3000mhz
1440p 144hz