Email vanishing a few seconds after being delivered. MacOS app issue

There is a serious bug affecting the email app on macOS. An email vanishes from the inbox a few seconds after being delivered on the iPhone if the email app is open on my Mac. By "vanishes," I mean it appears as if it was never delivered—it cannot be found in the bin or any other folder.

I tested this with a flight reservation email. Fortunately, I could resend the email, but every time I did, I received the notification on my iPhone. However, if the email app on my Mac was open, the email disappeared after 2 seconds.

This issue occurs only when the app on my MacBook is open. It is worth mentioning that the email was sent to an address generated by the "Hide My Email" option. Also I don't have any particular rule enabled that could cause this. The filters I have enabled would move an email to the bin folder.

This is a serious issue and needs to be fixed ASAP.