How can I unlock a "re-locked" phone (from outside the US)?

[AC Question]

My carrier is Sprint and I have a Motorola Moto X which was previously unlocked. I had been using a local SIM card when outside of the US and changing it out for the Sprint SIM card when in the US. This week, I discovered that the phone was again locked when I could not get local phone service using the local SIM card. Sprint has unlocked the phone (again) but not while I was in the US, yet the device status says it is still locked. They did mention users of this model have had problems after a recent Motorola software update. Fact or rumor? Motorola gave me instructions to do a recovery to "wipe cache partition" but no luck. For now, I am able to use the new add-on Sprint Open World plan (at no additional charge) which partners with a local carrier to provide unlimited talk and text plus limited data. However, ideally I would still like to use my local carrier because I already have a local contact number. Has anyone had a similar experience and been able to unlock their phone (not using a third party unlocking service)?