Upload does not work

Hii,
Upload of a CSV file does not work on any of my wordpress sites.
CHMOD is set to 755 or 777. With the Older 3.x version it works perfect!
If chose the file and click upload but nothing happens (Load 0 %), if i drag and drop it into the field, my browser wants to download the file.
i also try it on different computers and browers.
greetz

https://ww.wp.xz.cn/plugins/wp-ultimate-csv-importer/