I understand that, but I think I have difficult conditions in my case - white snow everywhere, clouds are white too and time is about 1 pm. As I see, ND32 is more suitable for strong sun or isn't it?
It all depends.
You shot that footage with a ND8 at F5.6, 1/50, and ISO 100. All else equal, if you used a ND32 (2 stops stronger than a ND8) and F2.8, (2 stops wider than F5.6) the exposure would be identical. So you have some flexibility there. There is no specific ND filter for a specific condition, it very much also depends on your other camera settings and what you are trying to achieve. The value of the ND filter has nothing to do with whether or not it's sunny or cloudy, you simply use them to alter your exposure based on the brightness of the scene and your desired camera settings. To put this another way, you could be in dark shade, but if you had the camera set to F2.8, 1/10 shutter and ISO 6400, you would probably need a ND64 or higher to get a normal exposure - even without any sun. Think of the ND filters in terms of exposure (the combination of the scene, and aperture, shutter speed, and ISO), not in terms of weather.
In my opinion your footage was fine, other than that it was unprocessed and overexposed. To remedy those two things, you will want to add a stronger ND filter (if you want to keep with those camera settings), and you will want to color grade and process that footage after the fact. If you don't want to process it manually after the fact, you might want to get out of D-Log and let the drone process it for you. If you don't want to use a stronger ND filter to reduce the exposure, your options are to use a smaller aperture (not recommended) or increase the shutter speed (you have a bit of leeway here, but it's up to you).
The other thing I would suggest is turning on the histogram - a scene of pure white snow fools the camera's meter into thinking it's brighter than it is (Even on a $5,000 DSLR it does this), so the EV calculation may not be accurate. You can trust the histogram.
You also mentioned your filters are polarized, so what is going to happen is any time you rotate the drone, your exposure is going to change. Polarization is strongest 90 degrees from the sun, and is completely eliminated at 0 degrees and 180 degrees from the sun. If the sun is directly overhead this is less noticeable, however as the sun gets lower it is very apparent. I would suggest not using polarized filters unless you have a very strict pre-planned flight path, otherwise you risk having uneven footage every time the drone changes orientation.
