OK, here is again the same problem I experienced while working on my project. This time it happened to the different Apps so this is totally replicable. It seems to be co-related to replacing the Grid/Form LINK. It really doesn’t take much time to replicate it.
I have a GRID / FORM Apps. They are stored in separate folder (say FOLDER1).
The two App are called Form1/ Grid1
I copied the two Apps within the same folder first (created Fom1cpy / Grid1cpy. First of all SC did not asked me to modify the LINK. After looking into Form1cpy I noticed the LINK still shows Form1 (not the Form1cpy) as an edit form.
I moved those 2 Apps to another folder (say FOLDER2). Modified the link to point to Form1cpy (instead Form1), generated code and now the ADD button is missing again.
I did some further testing and it seem that this problem happens when the FORM (in this case Form1cpy is not generated after renaming it. I removed LINK, regenerated both grid and form, then re-added the link with the proper settings and the ADD button appeared.
This seems to be work-around but the renaming procedure has to be re-tesated because when copying/moving Apps something wired happens to the LINKS.
I will do more testing in the future although those who do not know how and why this happens might be pulling their hair out screaming for help because this is so critical. I’m not sure that the workaround that I discovered will work all the time or I was just lucky in this case, so if you’re missing ADD button try this and see it this will work for you.