Good evening Philipp and welcome back!
First off, I would like to apologize for the delay answering.
We are currently experiencing a higher level of requests than usual.
Please rest assured that we are working hard at correcting this situation.
We appreciate your patience while we try to normalize things.
Could you please send me a copy of the latest version of your WordPress theme / child theme via a link to a .zip file link (stored Dropbox or Google Drive) so that I can run some tests on my end ? I recommend a private reply for that purpose.
Please ensure you are using the latest files as found on your actual website.
This way I will get access to any updates or customizations you might have made.
Secondly, could you also send me a copy of the csv file you are trying to import ?
Based on the limited info I have, it sounds like there could be either a conflict at play or some issue with the CSV file itself.
Hang in there!
Geoff B.