Carrier name in the status bar not showing
From searching around the internet I found a few users were experiencing this bug on iOS 12. If it comes back, you can update to iOS 13 and that should fix it.
You can also Update Your Carrier Settings:


Make sure your device is connected to a Wi-Fi or cellular network.

Tap Settings &gt; General &gt; About. If an update is available, you'll see an option to update your carrier settings.



It could also be an issue with your carrier.