not getting notifications on iphone se from one person

Glad that answered your question.

The person getting a new Apple ID must thoroughly cleanse her/his iOS device(s) as follows:

What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

Might you be sharing an Apple ID with that person? If so, stop doing that immediately.

another possibility is that they are blocked or muted make sure that they aren't

another possibility is that they are blocked or muted make sure that they aren't