My phone received a system update last night.
It took a long time to install and it made me fear that it had bricked my phone. Fortunately, it eventually finished and all is well.
It's still on Android 9, so I can still manipulate which LTE band I'm using. I would have hated to have it update to Android 10 and lose access to the radios.
I'm guessing that it was a security update of some sort.
FYI.
Update: Just received the same update on my ZTE Blade A7 Prime, as well.