Dimmer switches use phase control to chop parts out of the AC sine wave in order to reduce power.
Most out there are leading edge, meaning that they progressively chop the leading edge of the wave off. These are most suitable for inductive or resistive loads like your normal incandescent bulbs. Because they have an abrupt voltage change at the start of the wave they can cause buzzing at low settings.
For LEDs which have predominantly a capacitative load you need a trailing edge dimmer. This progressively chops the rear part of the wave so are smoother and allow for lower dimming.
The dimmer switch itself may need a certain amount of current to drive it, so if the load on it is too low, as in the case of LEDs, from start it lights the LED, then the load goes too small to drive the dimmer and it cuts out, followed by start up etc. causing your flicker.
In our office here I use a conventional dimmer which caused flickering. It could have been fixed by having loads more LEDs on the dimmer to get the load high enough. This usually isn't an option.
I fixed it by adding back in a small resistive load on the end of the LED run. Leaving one normal incandescent bulb on the run also fixes it but looks odd because of the difference in colour etc.
Basically I bought some resistors and heat sink and put them in parallel with the end LED. Because they are behind a ledge they are out of sight and can cool without fire hazard. I added just enough resistance to prevent the flicker on lowest dim setting.
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Dimmable bulbs and three way switch new
Dimmable bulbs and three way switch new