Amazon/Lowes says the bulb is dimmable to 10%. Anything below that will cause it to freak out, and most likely that is what you are seeing. The dimmer steps down 1% at a time.
On/Off instant while retaining dimmable from the switch is not possible.
Options:
Go with an on/off switch
Use different bulbs
Try tweaking the dim rate with Enhanced Dimmer (10% steps, delay of 10) which will ramp the light up and down in about a second, delay of 5 is about half a second. May remove the flicker. May need to try different settings.