If a chat message you sent doesn't appear as read and nothing else appears by it, it may be due to one of the following reasons.
Your network connection is unstable
With an unstable network connection, it may take some time for a chat to show up as read.
The recipient didn't see the message due to their use of the LINE app
If the person you sent the chat message to changed devices, reinstalled LINE, or accidentally deleted their chat history before checking the chat, they may not have noticed that they received the message. If the read mark still doesn't appear after some time has passed, try sending the message again or asking the person if they received it using a method other than LINE.
If an icon appears next to the chat message you sent, check its status by referring to this Help article
Let us know if we can make it better.