I suggest that when u back out of an individual text conversation that the list of conversations automatically scroll back to the top. This way you'd see the dots that indicate new messages. I have missed/had a delay responding to many new texts because I thought the list I was looking at was at the top. I often refer back to old text conversations lower down in the list and the screen remains there when I press the back button. This gives the I'm prey that there are no new messages.
Yes, there is sometimes a notification sound, but it may be loud in the surrounding area, or my phone often is on silent or vibrate.
I experience this issue I'm describing daily, and have to deliberately be mindful to actively scroll up.
Thank you