So, problem solved but not sure why. Here is more info in case someone else has this problem as I called into Apple Support yesterday and after 45 minutes with a tech, they could not explain why I was having a problem. They suggested a hard reset to see if that would take care of it. Didn't like the nuclear option so tabled that.
First, understand that my iPad is WiFi only, no cell connection. Also, the only sound/banner notifications that were being blocked were text messages. Other notifications like email, CNN, etc. would come through fine on my iPhone (8) even when I was using my iPad.
Resolution - I checked the Message setup in the Settings app on my iPad and the first option of iMessage on/off was set to On. I never use my iPad for text messages and so clicked that to off. Had my daughter text me a test message and BING, iPhone sound and banner went off like normal even though I was active on my iPad. Have had several other text messages today, all came through without a problem while I was on my iPad.
So, not sure why having iMessage active on the iPad silences notifications on the iPhone, but changing that setting has solved my problem.