Using "Change location..." (to the same airport) does reset the lagging as well.
When I'm starting a fresh new SOLO game with say 10 Aircrafts, I notice a periodic lagging which occurs every second. I notice it when I drag the radar screen very slowly. Actually, the interval depends on the Radar Sweep interval. When I increase the Radar Sweep interval to 5 seconds (I normally play with 1 second) the lagging occurs every 5 seconds. When all aircrafts are gone (I'm playing APP and I send them out of radar range where they get lost) the lagging will still occur in the configured radar sweep interval. Stopping and restarting the SOLO game doesn't reset/clear the lagging, even when starting with 0 aircrafts.
When I start a fresh new SOLO game with 0 aircrafts, I don't get any periodic lags, since there aren't any aircrafts and it's a fresh application start without any previous game sessions (and their aircrafts).
On a random side note: Changing the radar sweep interval mid game doesn't affect the radar sweep interval. Only restarting a SOLO simulation uses the new configured radar sweep interval.