Which Sim are you using?
Are you sure it's the update?
I remember there was LTE issue on Nokia 7 plus which was fixed over OTA update.
I have Nokia 6.1 and it's working fine for me atleast on the sim which I'm using.
Try restarting the phone and it may work.
I am having the same issue. But instead of 4G lte issues ..my phone starts to restart automatically once i update my phone to may update v2.22.
Even service centres are unable to pinpoint the problem. They asked me not to update the phone and wait for Android P update. Once they reboot my phone to the stock version it starts to work properly. But as soon as i update it. The problem persists. I have contacted the customer care. Ur service centre. Ur public forums and even the nokia Twitter handle. Nobody seems to know anything about this.