Upload stops with many small files


I have a little problem with Nextcloud 13.0.4. For many image uploads, the upload will eventually stop. I would like to upload 500 pictures and about half of it does not happen anymore. There is no error message. Also not in the log files. it just stops and does not happen anymore. Only the remaining time is showing. Does anyone have similar problems? Uploading single large files is e.g. no problem. There are even 8GB. Here is my PHP Config.

System: CentOS 7 with Plesk