Searching in Mojave Mail.app not working

Hi,

It looks like searching in Mail.app is not working correctly for me.

At least not like it was in High Sierra.

Even if I have a message open and search for the sender the search results will not show me the message.

I have tried deleting the Envelope Index files in the Maildata folder and letting Mail re-import the messages.

I have disabled the accounts and redownloaded all messages.

Nothing seems to work.

Any ideas ?

Paul