Although it might seem like a forgotten issue, the problems with notifications in MIUI 12 related to WhatsApp or other messaging apps still exist. This problem has appeared in many smartphones of different ranges with MIUI 12. The error prevents the notification of corresponding WhatsApp messages from showing and instead shows us previous messages that we have already read.
Solution
By now many users have tried to reset the device, delete the application and reinstall, without finding a solution to the problem. The only thing that seems to work is to block the app in multitasking , to prevent it from closing in the background and the notifications we receive are those that correspond. You just have to press and hold your finger on the app and choose the lock.