Permalink Redirect not working at upgrade

I recently changed my permalink structure so that it just has the post name rather than the month/date previously used on winetoweightlifting.com. I added this to my .htaccess file:

#RedirectMatch 301 ^/([0-9]{4})/([0-9]{2})/([0-9]{2})/(.*)$ https://www.winetoweightlifting.com/$4

and it worked excellently.

Now, it has stopped working and I am receiving 404 errors. And the only change I can see that happened was updating the WordPress.

Can someone help me pinpoint the error or how to rectify it? Blog traffic has plummeted!