E-Mails disappear in Outlook

Hi there,

since about one year I am experiencing a strange behavior of my Outlook app.

It is platform-independent whether I talk about Outlook on my proprietary Windows 11 Home computer or my Outlook Android app.

This morning - the best example. I receive a message and see it in my inbox. I then click the reply button and compose my reply. While I'm still writing my reply, I see the original message disappear from my inbox. This email is gone and cannot be found in any of my folders. Nowhere - neither on my PC nor on my smartphone.

If I check my icloud inbox online via a browser, the message is there in my inbox.

Can anyone tell me why emails are randomly disappearing? I'm getting desperate.

Many thanks for your ideas and best regards,

Rainer