You do not understand how the time-tracker works.
It was working properly.
The tool is NOT a timeclock. It does not simply allow you to clock in and clock out. It measures activity levels, and intentionally drops time blocks during which user activity was not detected.
You are welcome to learn more about it, or ask questions here.
Screenshots are taken when you are actively working on your computer/laptop while tracking time with the Upwork Dekstop App. The App doesn't track time for periods of inactivity when there are no keystrokes or mouse clicks. So you not working on the computer where you are tracking time can be a reason for missing segments. I would also like to add that adequate activity levels are necessary to qualify for the Hourly Protection.
You may refer to this help article for more information about logging time on Upwork.