I can't confirm this issue. For me, the A300 is running like a charm.
Most settings on Ultra with DX12 and FG on. Using RTX4080 and Intel I9 13700
Flown a lot of flights 3h+ and no FPS drop or CTD.
Starting, landing at EHAM, EDDF, EGLL or ESSA causes no studders.
Maybe worth a test to fly only the A300 and the two airports you want to see if the culprit, another addon.
Will say there are only a few pilots with the issue and not thousands of them.