Some Text Messages are appearing on my IPad and not my IPhone 11

To use SMS/MMS messaging from the iPad Messages App, your iPhone must be logged-in to iCloud with the same AppleID - and message forwarding to your iPad must be enabled on the iPhone.

https://support.apple.com/en-gb/HT208386

Also ensure that Messages for iCloud is enabled on both iPad and iPhone:

Settings > [Your Name / AppleID > iCloud > Messages - set to ON

On you iPhone, go into Settings > Messages > Send & Receive --make sure all the addresses are checkmarked in the top list labeled You Can Receive iMessages