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ITS_PRADEEPVISHWAKARMA
User level: Level 1 (12 points)

iPhone 15 cellular network unstable and drops after iOS 27 update

iOS 27 Cellular Network Instability – Network Keeps Dropping and Calls Affect Reconnection




Hi everyone,


I’m experiencing a serious cellular network issue on my iPhone 15 after updating to iOS 27.0. Everything was working normally before the update.


The network keeps automatically refreshing/re-registering. For example, the phone may show 5G/True 5G, then suddenly switch to No Service/no signal for 1–2 seconds, then the network comes back again. This keeps happening repeatedly. Sometimes the network may remain available for a short while before dropping again.


There is another unusual problem with calls.


If the network comes back and I immediately make or receive a call, the call connects normally and I can continue talking. Even if the network indicator becomes unstable during the call, the call itself does not immediately disconnect.


However, as soon as the call ends, the cellular network disappears again and the phone returns to No Service. The phone then has to wait until the network automatically comes back before I can make or receive another call.


Because of this, I sometimes have to wait for the network to appear before making a call.


This is not a situation where the phone stays without service for 4–5 minutes. The network can change very quickly — for example:


5G/True 5G → No Service for 1–2 seconds → 5G/True 5G → No Service → network returns again.


I have already tried:



  • Network Settings Reset


  • Restarting the iPhone


  • Completely powering it off


  • Factory Reset


  • Testing both 5G and LTE


  • Testing a Jio SIM


  • Testing an Airtel SIM

The same issue occurs with both Jio and Airtel, while the Jio SIM works normally in another phone.


I also ran Apple Mobile Diagnostics multiple times. Every time, it reported:


“Diagnostics detected a software issue.”


The diagnostic screen showed iPhone Hardware as passed/green, while Mobile Service was flagged.


I have also noticed unusually high battery drain with very little usage.


Has anyone else experienced this exact behavior after updating to iOS 27.0, especially the part where an ongoing call can remain connected but the cellular network disappears again immediately after the call ends?


Could this be related to the iOS 27 cellular/modem software or network registration process?

Posted on Sep 27, 2026 8:55 AM

5 replies

Jeff Donald
User level: Level 9 (64,078 points)

Sep 27, 2026 11:20 AM in response to ITS_PRADEEPVISHWAKARMA

There are several reports in the community of other members experiencing the same issue. It’s a possible bug, but better to error on the side of caution and get your device properly diagnosed.


Please have Apple perform diagnostics on your iPhone. It can be done in person at an Apple Retail Store or at an Apple Authorized Service Provider. You can also contact Apple Support and request remote diagnostics.


If you’re in the US, please call  1-800-MY-APPLE, or outside the US, consult the support articles below. In Canada, call 1-800-263-3394.


Contact Apple for support and service - Apple Support


Genius Bar Reservation and Apple Support Options - Apple

Hohohooooo
User level: Level 1 (18 points)

Oct 28, 2026 12:34 PM in response to ITS_PRADEEPVISHWAKARMA

My issue was resolved after reactivating both SIM cards. I converted my first SIM card from a physical SIM to an eSIM, and my second SIM card from an eSIM to a physical SIM through my carrier.


After setting up both SIM cards this way and inserting the physical SIM into my phone, both cellular networks started working again as they did before iOS 27.


I tried everything, but this was the only solution that worked for me.

Mstoutenburg
User level: Level 1 (8 points)

Oct 3, 2026 3:40 PM in response to ITS_PRADEEPVISHWAKARMA

After I updated this has been happening to me but my network never comes back. Before the update I was on 26.1.2 and never had a lte issue. It has been reported iPhone 18 and AT&T has cellular issues losing signal completely as well.

ITS_PRADEEPVISHWAKARMA Author
User level: Level 1 (12 points)

Oct 3, 2026 4:53 AM in response to ITS_PRADEEPVISHWAKARMA

Thank you for your response. I have already run Apple Diagnostics multiple times. Each time, the diagnostics completed with the same result: “Diagnostics detected a software issue.”

In the results, iOS Version and iPhone Hardware showed green checks, while Mobile Service showed a warning.

I have also tested both Jio and Airtel SIMs, on both 5G and LTE, and the same issue occurs. I reset Network Settings, restarted the iPhone, powered it off for several hours, and even performed a factory reset, but the issue remains.

The problem started after updating to iOS 27.0.

Could this indicate an iOS 27 cellular/modem software or network-registration issue? I would appreciate any further guidance on what diagnostics or steps I should try n ext.



ITS_PRADEEPVISHWAKARMA Author
User level: Level 1 (12 points)

Oct 3, 2026 4:56 AM in response to ITS_PRADEEPVISHWAKARMA

I also noticed unusually high battery drain after the iOS 27.0 update. Even with minimal usage and the screen mostly off, the battery drops significantly. I have also tested with Airplane Mode and Low Power Mode enabled, but the battery drain still seems higher than expected. Could this battery drain be related to the same cellular/software issue?

Originally posted at discussions.apple.com/thread/256365999