Having higher sessions than clicks is normal behavior and indicates positive engagement with the client's website.
Suppose a user later returns to the website (e.g., the user enters the client's website URL or has the website bookmarked), instead of any other referral information. In that case, these additional sessions have their campaign source reported as the last-known campaign source. In this case, the last-known campaigns are the TTD campaigns.
Each direct return session after the initial click is another session attributed to our campaign(s). This is a scenario where a single click leads to multiple sessions in Google Analytics.
Tip: The client can use advanced segments to view new vs. returning sessions for a campaign and confirm that the larger number of sessions is partially due to returning users.
For any additional GA questions, please review Google Analytics FAQs article