WhatsApp allowed you to archived messages you no longer follow. This is a way to hide old messages. But not completely delete them in case you need to access them again in the future. However, the annoying feature is that if another participant sends a message in an archived chat, the message gets dearchived automatically.
There is some good news from that front. As WhatsApp has announced it will be rolling out a new setting that will allow users to process archived messages. With this change, users can now choose to hide and mute archived messages, or keep the app’s current behavior.
If the user selects the former, it means that the thread from the archive will still be archive and kill even if it is active again so no editing has needed. However, if they wish to join the chat, they can do so by manually archiving it. We’re not sure why WhatsApp took so long to roll out this feature as many people have expressed their frustration at dredging up unsolicited archive messages.
These changes should have been posted already. So make sure you have the latest version of WhatsApp if you want to take advantage of them.