irregular sale

Leave well enough alone.

If Adobe Stock detects an issue, they'll do what needs to be done. Let them handle it.

It is unlikely that fraudulent licensing activity would occur on the account of a Buyer with a Custom subscription.

I suppose another option is that a buyer may be using up their credits prior to discontinuing their stock account.

If different items are being sold then there should be no issue in taking it as normal but if it is the same item then it could be a matter of concern however the number is not that high either.

Nothing, but 17 downloads at nearly the same time is not a lot. Was it the same item?