This isn't really the appropriate club; you would be better off posting in the Android club or using the Report Problem option on the app.
That said, you you tried clearing the application cache? If that didn't help, uninstall/reinstall? I haven't seen many issues receiving notifications for messages on the app.
I will get alerts on my Android for messages. I will clearly see there is a new message in the list, but when I try to open the individual message, it isn't there. If I go to my desktop, there is no issue. I wanted to see if there is a way to add a refresh button or if something can be done to improve the communication in real time. I have already tried uninstalling and reinstalling and I have made sure I am up to date.