Messages not sending all my texts to one specific user

I upgraded to a new iMac running Catalina. Since I've done this I'm having a problem sending messages to my daughter and maybe others. At first she received no messages from me, but other people did. I fixed that problem using a solution from Ask Different. I thought the problem was solved. But now I found out that about a third of my messages don't get delivered to my daughter. We text several times a week and before my new iMac everything went thru fine. I text from my iMac, my iphone, and my iPad and in the past all three worked fine. Now they don't. It could be my daughters phone but it only happens with me. and likewise, as far as i know it only happens when I send to her. She doesn't receive it at all. Has anyone else had this problem or does anyone know what is maybe causing it?