Replaced display assembly (LCD+Digitiser) but Touch non op!

I’ve replaced a few series 2 screens before with no problems.

however, I now have one series 2 38mm with a brand new display assembly fitted but the touch is non op! Screen is working fine but does not respond to touch.

I have another new display assembly (complete LCD +digitiser) and it’s the same. Touch non op.

I also have 2 42mm Apple watches now! And I have one brand new screen, fitted it. Touch non op! Fitted to the other 42mm. Touch non op!

Does the new screen have to be coded in or something? And why was that not the case for the others I’ve done?

any help much appreciated.