Hey guys @redrob, @chon59. I believe I figured out how to make the free orders work on new versions. I did this test on PS version 1.7.6.5 so if it is the same as your versions hopefully it will work. Prestashop changed the core.js file all around and made it much more difficult to read and adjust. I did this test with a new installation of Prestashop running in a virtual machine so no guarantees it will work with production environments.
File to change: core.js
File found in: /themes
Roughly line 161
The code is all on one really long line. Easiest way to find the spot is to search for: var e=(0,r.default)("body")
There will be 2 results, the one you want is the second one on line 161 which is a good ways in the line.
In the same line right after, var e=(0,r.default)("body");
insert the following code
if((0,r.default)('input[data-module-name="free_order"]').length){this.toggleOrderButton();}
After making this change you may need to clear Prestashop's cache under the Performance settings.
This should allow free orders to be processed now. Hopefully this works for everyone.