Please click Overview under each and every module to show the list of units. To the right of each unit, there should be a check icon to show it is complete. Look for ones that don't have a check, and when you find one, click into that unit and complete it, making sure to click unlock achievement as needed. Once you have completed the unit, return to the list of modules, refresh the page, expand Overviews again, and again look for units that don't have check and repeat.
When ALL of the modules in the list don't have any units without check next to them the 8300 XP should light up.
What you are seeing is typically caused by a module/unit being updated by Microsoft after you completed it.
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