Bob,
what you experienced is a common problem called "uplift".
Any structure has the ability to have that effect if air can get into it or under it.
Even a pole barn open on all sides can be lifted, hence the need for "hurricane ties" in any structure to tie it together.
Seen too many structures that are poorly built and building inspector has missed that detail.
Your "sheds" are "temporary" so fall outside the building code.
You were lucky to keep them in place.
R
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