Poor reception on Nokia G42

I bought my parents a G42 each at the same time. One of them broke the screen, which I replaced. That same phone is now on the same network as the other and we've noticed that it gets a much worse mobile connection than the other phone (that never had any bits replaced).

For example, the repaired phone only gets Edge but the "untouched" one gets 5G in the same location.

The repaired phone has only recently been changed into the same network as the "untouched" one, so it might well have had a signal issue for a while, possibly ever since I repaired it.

Can anyone advise what the best resolution is? For example, I wonder if the antenna is on the back panel, and perhaps the contacts between this and the main board need cleaning?

Thanks for any help and advice!