Inbox on Mac Mail Refreshes Every Time I Send Or Flag an Email

Whenever I send or un-flag an email my entire inbox flashes and refreshes. This has only been a problem since I purchased my new MacBook pro.

It's the same issue that was reported here but no resolution was found...

Why am I experiencing a list refresh when… - Apple Community

It wouldn't normally matter but the refresh is lagging and because I filter all my emails by unread, i'm a few sentences into the next email when it disappears and opens the next unread email.

How do I stop this from happening.... It seems like a bug from the software rather than any conflict caused by other apps (mainly because it's been happening since I purchased the new computer).