Diagnosis
This is almost always a weak connection or a failing component on the power supply line that feeds the LED display. It's getting enough juice to run the motor but not to power the display consistently. Loose ribbon cables or solder joints are common culprits.
How to Fix It
Unplug the fan. The display is part of the top control panel. To check connections, you'll need to carefully open the upper housing. This usually involves removing a plastic cover held by clips and a few screws. Once inside, look for a thin, flat ribbon cable connecting the display board to the main board. Gently unseat and re-seat this connector. Also, look for any obviously cracked solder joints on the display board.
If That Didn't Work
If the connections are solid, the voltage regulator or a capacitor on the display board is likely failing. This is a component-level electronics fault. You could try replacing the entire display/control panel assembly if you can find a spare part, but it's often not cost-effective.
Heads Up
When handling the ribbon cable, don't touch the gold contacts with your fingers. The oils can cause corrosion and a poor connection over time. If you must clean them, use a q-tip with a tiny bit of isopropyl alcohol.