This is likely what Sig originally listed the M17 as including but if you look through these retailers listings it has obviously changed a few times, some list this as including 2-17rd magazines only, some have it as 2-21rd and 1-17rd while others list it as 2-17rd and 1-21rd. So if you find one in stock that you decide to purchase you can always contact the seller and verify what magazines come with, another possibility that Sig and Springfield have done is they'll include less magazines then they typically offer but give you a certificate to send in for additional magazines free of charge, they do this when production can't keep up with demand.
But look through the listings here its all for the same upc, same model number, but different accessories on most all of them.
The last year has been crazy and manufacturers have had to modify how they do things to keep up.
https://gun.deals/search/apachesolr_search/320f-9-m17-ms

Pauli, Sig Sauer Customer Service can best answer this (with the UPC code) at 603-610-3000 option 1 Monday-Friday, 8:30am-5:00pm EST.

The M17 and M18 used to come with three magazines, but they're currently only shipping with two.