It seemed to be working with my alternative code on my local test site, regardless of whether Forms is active.
When I went back to your site I noticed something which I had somehow missed before, namely that your page currently has JS errors on it. See screenshot.
That is without Toolset Forms enabled.
Errors in one part of JS code can have knock-on effects in other parts of code, so it's not possible to debug this further until those errors have been resolved.
Please investigate and fix those errors, and then I can resume trying to identify the form-related issue, if you still see it. After fixing those errors you may not.
I've tried to reproduce the problem on a test site based upon what you've provided and not been able to, and I don't think I can do anymore without a copy of your site.
So let me ask again if you can provide a duplicate, and if so I will probably pass it straight to my colleague in second tier who can spend more time looking into this.