SIM celluar data works in iPhone 7 but not in iPhone 8

I have a SIM with Voice + LTE Data.

With the SIM in the iPhone 7, voice and cellular data work (for example, can browse using Safari). The carrier icon says "LTE".

With the SIM in the iPhone 8, voice works, but cellular data does not. ("Could not activate cellular data data network"). The carrier icon says "3G".

The phones are not locked to a carrier. I have re-installed iOS. Checked that LTE is on.

Any ideas on how I can troubleshoot this?