Hello James,
thank you for your reply. I did as you suggested and found out that the problem was caused by a plugin (Advanced Custom Fields: Contact Form 7 Field). I had integrated it in my theme so I was able to commented the lines which caused the trouble out:
$(".cf7-select").select2({
width: '100%'
});
Since this is only showing a more fancy select dropdown in backend it’s causing no harm :).
I still don’t really understand the problem behind it as it was triggered by the new ACF Pro Version.
Thank you for your help
Britta
