Morning Mr. Pepe,
Thanks for the video .
Often when shaking the grate it will do just as designed and release the ash and small fine material at the grate allowing the gasifier to breath easier . This in turn will though the fuel / air mix rich. By adjusting the air mix at the same time shaking the grate the mix may stay correct .
Also many times when shaking the grate the fines fall out and small char from above will quickly fall in it’s place and maintain the same vacuum or resistance thus keeping the correct air mix.
I think in the video when the motor was about to stall it was because of too rich gas mixture .