Thanks for the comments. Yes, I did all the steps above but to no avail. However, after reinstalling the app several times finally the problem was solved. Now, I am facing another problem. The app would freeze every now and then. One problem after another. Yeah, I totally agree with you. They should get the basics right first.
I am a Premium subcribers and I have downloaded and sync my notes on the iPhone using WiFi. When the syncing has finished, I still cannot access most of the notes from the notebook that I made available offline when I off the WiFi. I tried clearing the cache, signing out, reinstalling, nothing seems to work. I have contact support and still waiting for a reply. Meanwhile, has anyone got any solution to this?