Again you brought me on the trail of something 😉 acf_form redirects to the page where it was called on with a $_GET parameter of ?updated=true by default. To handle this on my own, I had to explicit set ‘return’ => ” in the options array of the acf_form.
The longer I work with acf, the deeper I get in. And my combined form works like a charm now.
Thanks for the support!