F-117 needed a bigger tail after the prototype flew. Did the Lockheed engineers not know what they were doing? What about the control surface changes from FC-31 #1 to #2 to different F-35 prototypes? Did the engineers at Shenyang not know what they were doing?I think I'll trust the engineers at Shenyang to know what they're doing
As much as you simulate and test, sometimes you have to revise a design in light of flight testing. Sometimes shit happens.
Equally, maybe an apparently odd pattern of movement is a software bug, or even a deliberate test. Its in very early stages of flight test.