Exclamation mark on my message icon, messages alternate from green to blue

For at least the past year the texts between my mom and I alternate from green to blue, sometimes the app icon will show a red exclamation point but the messages always send whether SMS or Imessage. We have both looked into remedying this many times. Our setups are correct. My mom doesn’t block me either ever. It is driving us nuts because this has been an issue for a long time. Again, they alternate back and forth from green to blue, then blue to green etc. Any other ideas?