Cellular data not working on iOS 26.1, iPhone 15 Pro Max

Have you tried this

Settings > General > Transfer or Reset iPhone > Reset > Reset All Network Settings

It could possibly fix your mobile data. However, doing this Forgets all WiFi Networks so you'll have to manually reconnect

“Cellular data not working on iOS 26.1, iPhone 15 Pro Max: Updated my phone to iOS 26.1 this morning and then my phone started having intermittent cellular signal. I use both a physical and an e-SIM and both have had signal issues since the update. I also only get EDGE speeds for my data even though I’m on 5G and I still have a few GBs left on my data pack. When I try to use Safari, a popup says ‘could not activate cellular data network’z Have any of you experienced this also?“

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Troubleshooting iPhone Cellular After an Update:

Visit these Links:

• Calls: If you can't Make or Receive Calls on your iPhone - Apple Support

• Messages: If you can't Send or Receive Messages on your iPhone, iPad, or iPod touch - Apple Support

• Errors:  If you see a Cellular, Ultra Wideband, or Apple Pay Issue Message after an iOS Update or Restart - Apple Support

• "No Service": Is "No Service" shown on the top-left corner of your screen? If so, go here to fix this: If you See No Service or Searching on your iPhone or iPad - Apple Support

• "No SIM": If "No SIM" is shown on the top-left corner of your screen, go here to fix that: If you See 'invalid SIM' or 'no SIM' on your iPhone or iPad - Apple Support

• Report this to Apple:

Do your part: Let Apple know what is going on here. Provide them with feedback on this. They may not get back to you directly, but the more feedback they received on this, the more they will know what is going on, and what needs to be fixed in updates to come.

1. Go Here: Feedback - iPhone - Apple
2. Comment: that this all began after installing an update, and how you have troubleshot this, thus far. Include the URL of this thread.
3. Select: "Bug Report" for the "Feedback Type"
4. Proceed from there aw necessary

“Yes. Though it was an iPhone 17 Pro, and I now have no cellular connectivity at all.”

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Troubleshooting iPhone Cellular After an Update:

• Force Restart your iPhone.

Having just installed an update, start with a Force Restart. Go Here: Force Restart iPhone - Apple Support

• Report this to Apple:

Do your part: Let Apple know what is going on here. Provide them with feedback on this. They may not get back to you directly, but the more feedback they received on this, the more they will know what is going on, and what needs to be fixed in updates to come.

1. Go Here: Feedback - iPhone - Apple
2. Comment: that this all began after installing an update, and how you have troubleshot this, thus far. Include the URL of this thread.
3. Select: "Bug Report" for the "Feedback Type"
4. Proceed from there aw necessar

Yes.

Though it was an iPhone 17 Pro, and I now have no cellular connectivity at all.