Timatic, the database used by airlines, states:
Residents of Italy holding expired Residence Permits or a
copy of an expired Residence Permit are permitted to
re-enter Italy, provided also holding a receipt issued by
the Italian Post Office or Police Department, confirming new
permit has been applied for. Applications for renewal must
be made within 60 days of expiring, otherwise immigration could refuse re-entry, even if holding confirmation of application.
In other words, because you applied for an extension no later than 60 days of the expiration date and have a receipt of it, you can go back to Italy without issues, but not return to the Netherlands until the new permit has been issued.
In practice, however, there is nothing stopping you from flying between the countries. Being Schengen states, there are no border checks, only an ID check at the airport bag drop, and, except for Ryanair, easyJet and Wizz Air (in other words, do not fly with those), they only check you're the person on the ticket.
So like I said, legally speaking you have to return to Italy and wait for your new permit to be issued before returning to the Netherlands, but in practice nothing will prevent you from going back to the Netherlands straight away