Unable to connect yeelight bulb ver2 to wifi

I having difficulty to connect back all my yeelight bulbs to my wifi after router reboot and changed password. My current wifi is in 2.4ghz, and all other smart sonoff switches are managed to connect to my wifi ( i assume my router is working) except yeelight. very painful to connect this bulb to wifi each time.
Please help!

Did you try to reset the bulbs by turning them off and on again 5 times?

Below are the thing i had tried:

  1. reset bulb (on/off 5 times) and reconnect wifi again
  2. removed all bulb and reset one bulb and connect wifi
  3. tried move the bulb to beside the router
  4. tried forget my home wifi and connect to the bulb then connect to wifi
  5. tried singapore and china server
  6. Tried log out and log in xiaomi account
  7. uninstalled and installed yeelight app

Nothing above helps …