If I understand the problem right,,the toe plate itself is being bowed outward from the spring tension of the release rod/mechanism underneath it?
If that's the case,,the spring tension can be captured under the toe plate by a separate steel bushing or small plate installed in the wood and secured in position with a couple of wood screws. The spring would press against that secured steel abutment w/the rod passing thru it.
The toe plate would then mearly cover that up with the release button end of the rod extending thru the brass plate so you can get at it. But the brass isn't taking any pressure from the spring & latch mechanism itself.
If the box lid is bowed from the flat spring that pops the door open a tad,,then lighten that spring some, or even just change it's engagement angle to the lid so it just barely pushes on it as the lid is closed.
No need for it to do a Jack-In-The-Box routine when you push the release button below. Just enough power to gently pop it open.
If the door is too thin of material and keeps bending with normal use and handling but otherwise fits well,,you can soft solder a thicker piece of brass to the back side of the door itself to reinforce it. It doesn't have to cover the entire back side. From the hinge back as far as possible and perhaps a 1/2" wide is usually plenty. It doesn't take much to re-inforce it against bending. You may have to readjust the opening spring after adding some thickness to the middle portion.
If I misinterpreted the problem,,then disregard everything above and carry on!
