One reason why attribution activity is missing from the contact details might be because the lead fills out the form using iPhone/safari. And this issue happened because the User turns on the option to block all the cookies when form submission happens.
Here is the reference link: https://support.apple.com/en-in/guide/safari/sfri11471/mac
And one other case where we can't track activity, If
params are present on the URL. ex:
Cookies and local storage permissions are required. We are storing user's activity and server session-id on the browser's local storage. If session-id does not store on their local storage or if we can't access it, we can't store contact activity.
For the notes: we are storing every activity but not assign them to contact if the session is not stored or access.