Check to see if you have some kind of filter working. eg: Quick Filter Bar may have something selected which is changing the view. Example: you maybe you are only viewing starred messages.

Maybe you have got a 'Custom View' operating. Check out options : 'Menu icon' > 'View' > 'Messages' suggest you select 'All'

Have you selected to view in Date order so new mails show at the top or they are all lurking at the bottom and out of view?

Do you have threads enabled, so the new mail is hidden somewhere in a thread? You could try removing the threads option.

There is a quick method to show only new mail in a folder. Quick Filter Bar: click on 'Show only unread messages' icon - looks like a pair of sunglasses.

Thank you very much. The problem was indeed with Custom View. Checking "all" immediately solved the problem. Scristy