If the freelancer isn't providing a satisfactory explanation AND the amount of work actually being done seems low compared to the hours billed, then moving on might be the best choice in the long term.
Thank you for your comments.
I chose this freelancer to manage my Amazon account. This is quite a complex task requiring quite a lot of different skills. This freelancer had the team support to cover all aspects of the management of the account.
I understand your comments about getting several freelancers on board but it wouldn't have worked in this case.
I took a lot of time to chose this freelancer and really hoped I had someone on board for the long term. I really don't want to cut ties so soon but the low level of activity has led me to question the integrity of the freelancer.
In addition to what others mentioned. Does the work involve waiting around? An example might be if you expect a freelancer to be open during a certain block of time to quickly respond to customer chat requests, answer calls, quickly answer emails, etc. The tracker would not do well for work that involves waiting to be available as "activity" would vary day-to-day depending on how busy it is that day. I don't know whether that applies.
As others mentioned, the time tracker tracks keystrokes and mouse clicks. There are some kinds of work that don't show as high activity if the freelancer is not actually typing. I don't think the tracker can track work done on a tablet or phone either. I suppose you would know whether your project requires this kind of work, but sometimes clients (and freelancers) do not realize the shortcomings of the time tracker.