first of all I would like to tell you how great work you have invested in the qform form builder plugin. I use the plugin a long time without any problems. But now, after I have changed my wordpress site to ssl some of my users have problems by uploading files.
If I self tested the form, I have no problems. But in last time I get a few error notifications. I would thank you a lot, if you can get a quick overview. For example you can visit the following url, the form is insert: https://www.widerruf.info/kostenlose-pruefung-lebensversicherung/
I wish you a nice weekend and a good start in the upcoming week.
After I can´t fix the problem by myself, I have done a rollback to get the database strukture back to none ssl. After that the plugin works fine. But this is not the way I would like to leave the site in future. I will strukture the site to ssl. I will try your communicated option and will respond later, if the problem will continue to exist.