I doubt that’s the case, the experience is much better compare to early days for me

This is interesting. Are you saying because some user switch to safari during checkout and tracking lost here? Since cookie will be cleared. But how about these special query param as you mentioned? That still can be maintained for tracking?

UTM parameters can be identifying but not generally considered private - rather the opposite - so while you can link your cookie to UTM parameters and join with other UTM-keyed traffic data for useful results, you can't do the inverse and use knowledge of UTM parameters as sufficient proof to recover a session cookie.