Q: We replaced some damaged screen panels on our porch, and they are starting to come loose. What did we do wrong?
A: First, what you did right, you gave it a try. Sometimes, like learning to walk, we stumble a bit. Get back up and try it again. This is how we learn, so don’t be too hard on yourself.
I have two thoughts on your screens. First, why were they damaged in the first place? Kids and pets are tough on screens, and with new screen in place there is again something to get damaged.
If kids and pets aren’t an issue, then I suspect the wrong size spline was used and it’s not firmly holding the screen in the seating groove. Thicker spline is harder to work with, but more secure once seated. Give it a try.