Ok, at least we already got the assembly of the bed ruled out for now.
Issues that remain then is the wobble in your bed. Not exactly sure how to tackle that (except adding extra linear rails etc, but that should not be needed for 3d printing anything)
I looked at your video again (from the wetransfer link) and between second 6-7 there is a really short very quick movement/shudder that seems strange. It might be a small travel move or something, but it seems a bit awkward to me.
Did you ever share the generated gcode? I can’t seem to find it.
My bet would still be on something backlash related. It reminds me off this thread: A350 - Not printing perfect circles
You could try to fix it yourself, there’s a guide by @sdj544 here: Excessive play in x-axis linear module bracket - #9 by sdj544
This probably will void your warranty, so you might want to check with snapmaker support first if they can maybe identify the issue better.