Re-watched that video a bit more closely. Looks like the problem is in the lowest level. You don’t have foundations in the grassy/hill area. You have a few on the outer base of it with pillars coming down to the grass. Those pillars need to be connected to the foundations for the stability. You’ll have to add a higher foundation to the existing ones to bring them across the center basement area.
Did you happen to check the stability for the surrounding pieces with a repair hammer at any time?
Also, to prevent any possible issues with the building’s stability as a whole, it’s best to place your base foundations grounded and attach pillars to said foundations from the group up.