Anyone familiar with this issue? Payment shows successful in NetSuite but declined and cancelled at settlement in Cybersource - unfortunately, no one to contact and not much information about this process...

A little late so you might've figured it out by now - Is that payment actually successful? I see it has the handling mode of Record External Event, which means you're not actually processing anything, you're just telling NetSuite you used X payment method for a payment outside of NS. The entry with the handling mode of "Process" is the one actually hitting your Cybersource, which is coming back as a Payment Hold due to the issuing bank being "unavailable"