inbox disappears

My mail inbox label frequently disappears and so I cannot access my inbox. The only way to recover it is to restart the application.

Hello Alan,
what mail account does this happen with? Does refresh also resolve the problem?
Is there any error message when it happens?
If so, can you please copy the error message, please

Thank you for getting back to me. The account is with Virgin Media. Refresh can sometimes cause the inbox label to return, but often not so. There are no error messages.