I also believe that mobile connectivity depends on the provider. I am using both Xperia 10ii and 10iii l. I have a Vodafone SIM and a Congstar SIM and switched the SIMs between both phones for testing. Neither the 10ii nor the 10iii had connectivity problems with the Vodafone SIM. Both phones (the Xperia 10ii since 4.4.0.68) have connectivity problems with the Congstar SIM.
Curiously, an older Android phone needed a restart for adopting to the provider settings when I placed the Congstar SIM in the phone (that previously was used with a Telekom SIM).