I experience the same issue. The search bar (top-right) area disappears after the app has been open for X hours. If I close Airmail and then re-open it will appear. Kind of a pain and would like to see this fixed.
I have the same issue. This issue has been posted online long time ago. The administrator should pay attention to this problem as without searching function, reading a massive amount of emails is a huge pain. This could lead to the entire app become useless.