Mail previews are there but the actual message is empty

When Mail receives a message it displays in the preview pane, often incorrectly. Meaning the sender and subject belong to another email somewhere else in the mailbox. When you select the email it is blank for upwards of 20 minutes then mysteriously appears. Rebuilding the inbox or specific mailbox does not help. Restarting the computer does not help. Monterey 12.6+