In general there are a couple of legitimate ways this can happen - the first probably doesn't apply here given the time periods showing in the screenshots and the months in question, but could apply for other similar situations.
1. Users that post time on non-working days (maybe some weekend hours on the timesheet for example) will show posted hours in one week/period, but can appear in the project on the next working day, which could show as an increase the week after.
2. If the timesheet entries are fully financially enabled, and go through the financial posting jobs, an adjustment may be made that isn't reflected on the timesheets. Running the Import Financial Actuals job at that point can apply those adjustments to the project data (up, or down, or moved to other projects, etc.).
Just to be mindful of those things before chasing down other reasons.
If the issue goes the other way (more hours on the timesheet than in the projects), I would also check to make sure there are no Indirect time entries in the time sheets. Not all the company processes are always followed all the time