Thanks for the reply. I am familiar with how to change the "Open with" setting using get Info. There is something installed on my system that is changing this setting. I should not have assumed it is Affinity Designer. Do you have any other idea what it could be?
I'm using Afinity Designer 1.6.0 on an iMac, macos 10.11.6. I assume this happens after updates but I'm not sure. AD changes my system preferences and makes itself the default program for .jpg files. I am able to change it back but this has happened a few times. It's not cool to change my system preferences like this. I didn't notice anything in AD's Preferences that would affect this behavior. Is there a way to configure AD so it doesn't assume it's the default program for certain file types?