The first touch and last touch for associating contacts with a campaign is measured (as defined in this article) as "First touchnew contacts for a campaign are contacts whose first session on your site was associated to the campaign's assets. Last touch new contacts for a campaign are contacts whose last session on your site before their first conversion was associated to the campaign's assets."
You can expect the contact's last touch campaign to update if they are interacting with assets associated with different campaigns.
For more information on this matter, I wanted to share these resources: