Ceiling fan light flickers one time when fan is turned off with switch
i don't think there's anything wrong with it per se, that's just how it's made/designed. The cause is quite complex, but I'll try to explain.
Keep in mind that the built-in LED is very sensitive to even small amounts of power.
When you use the remote to turn it off, a tiny computer in the fan either tells the LED's DC power supply to turn off, or it disconnects the LEDs from the DC power using a transistor, and the light shuts cleanly off.
When you use the switch, that tiny computer is unplugged and cannot control anything, so the effect is indeterminate. There's enough residual power in the power supply that finds it's way to the LEDs without a controller controlling. It could even be generated (literally) by the fan still spinning, inducing a current that flows back into the incoming supply and drains the only place it can; the light.
At any rate, it's harmless, if annoying. You could hack apart the fan and make some adjustments to the circuitry, but that will void the warranty, bother your insurance, and risk breaking things, all for a rather small payout.