This is normal if you do a complete clear of any area maps because the experience (MSQ specifically) has been buffed with the release of the new expansions. Best thing you can do is have another job on hand as a “side quest” job, and one for your MSQ if you really want to do a clean sweep your first run through but not outlevel the Main Scenario. Or you can continue to clean your maps and see just how high you get before you reach another expansion—the latter is what I’m doing on an alt because I’m curious to see if I can hit 60 or even 70 before I get to Heavensward.