Buddypress Activity - Regen with new image sizes

Ok, so I’ve increased the dimensions of our medium size which is what the activity feed uses. I regenerated thumbs which created the new sizes that I can see in the ftp as expected. I’ve cleared my browser cache and firewall cache. But it will not display the new image sizes in the feed for existing images. It keeps showing the old image size (which are still on the server). If I delete the old image sized image out of the ftp hoping it will force it to switch to the new image… it just doesn’t display an image. If I check in the meta info of the media library it shows the correct buddypress activity size or whatever for that image so it seems to know the correct image it should be using… but it won’t.

If I upload a new image to the buddypress activity feed then it works as it should with the new image size.

I’m not sure what I’m doing wrong. Is there a way to force this to use the right image for existing images or what?