Hi, My messages from whatsapp keep deleting before i get to even open them. They sometimes appear on my screen but then when I unlock my phone and open the message they disappear

Hi,

My messages from whatsapp keep deleting, it has been going on for a very long time and it has become very frustrating. They sometimes appear on my screen but then when I unlock my phone and open the message they disappear. I have the most up to date whatsapp installed, and turning my phone off does not help much.

I would be really grateful if you could please help me fix this problem.
Kind Regards
Ariane