iPhone shows No Service when leaving WiFi and WiFi calling

[betamaxdroid]

I have a 6S unlocked on T-Mobile with iOS 12.01. When my phone jumps on wifi and connects to T-Mobile WiFi aka WiFi calling, it's unable to find service again on the carrier's (T-Mobile) network when disconnecting from WiFi. Let's say I'm in a building with wifi, and weak network reception. The phone connects to WiFi, jumps on WiFi calling, all is okay. When I leave the building, and the WiFi is no longer available, it simply cannot find a network again. If it's on WiFi calling indoors, and I disable wifi, it won't even attempt to search for a network; it just says No Service. I have to cycle airplane mode to force it. This is a new development with iOS 12.

I reset network settings, and also "restored" my iPhone (although I have restored from a backup as well, and re-wiped network settings, and all settings and preferences), to no avail. I'm dreading having wipe it and not restore mostly because of all the work I would have to put in to restore everything, and I don't even know if this would solve my problem.

I've tried many google searches, and I cannot find anyone describing a similar problem. Has anyone experienced this?

 

[imagineadam]

I’ve been having a problem ever since the update to iOS 12 on my 7 on att where it will randomly drop cell data and the only fix is to reboot. What triggers it the most is leaving or joining WiFi networks. Mine doesn’t say no service though. It will come back with signal but then it says I’m not connected to the internet until I reboot. Happens 3-4 times a day or doesn’t happen for a few days. It’s gotta be an iOS 12 bug. Here’s the other two threads about it.

https://forums.macrumors.com/thread...x-ios-12-gm-at-t.2138650/page-2#post-26691139

https://forums.macrumors.com/threads/still-randomly-losing-at-t-cellular-on-iphone-x-and-12.2138607/