Message delete

Is that a group message?

Do more with Messages

• Learn how to leave a group message, or add or remove someone from a group.
• Name your group messages to make them easier to find.
• Use inline replies and mentions to call attention to specific messages and people in your group messages.
• Explore the latest features in Messages to stay connected to the conversations that matter the most.

It would be better if you can please re-post with a screenshot, in order to understand the phenomenon better. Images/pictures speak louder than words. 

Please understand this is a public forum: While attaching a Screenshot, do not provide any personal credentials, such as IP address, Card detail, email id, apple id, IMEI number, Serial Number, Phone number, Order ID, if you are sharing a map ensure your location is not identifiable, etc.

With the limited information that you have provided, It is hard to even guess the problems faced by you. 

You may get faster and better responses to your query by --> Writing an effective Apple Support Commun… - Apple ...

Please re-post with detail so that someone else can help.