Same here. Took off from a crowded LFPG with a stable 35-40 fps, cruised 9 hours at 55-65fps, landed at TNCM in a stuttery mess of 20-25fps . Can’t imagine how bad it would have been landing at one of the busy US/CAN airports.
Oh, and I got ~75fps at TNCM after reloading
(5800x3d, 3080ti, 3400X1440 TAA, 200 TLOD and mix of ultra and high)