I see today that there is a new version of the plugin available. I am not sure if that fixes the problem.
I am not sure who to thank for this fix but;
If you go to your contact forms (not the code editor or anything like that) just the form you have made and add to the left side of the screen, into the form section
<p style=”visibility:hidden;”>[file upload]</p>
that form will work. You have to add it to each form that is not working.
I know this has been hard to solve for many people like me and I was grateful to find this fix even if it is not the proper fix.
Again, I am not sure if the updated plugin as of toady fixes the issue. It might.
Simon