Touch(): Unable to create file panel

Hello, I have a Kirby 3 install running on a shared hosting. Everything worked fine until no files could be uploaded anymore. I’ve increased memory_limit, upload_max_filesize and max_execution_time by php.ini. Everything worked fine. A few hours later it was impossible to login to the kirby panel. I’ve got the following error:

touch(): Unable to create file .../site/sessions/1234....sess because of Permissions denied.

I’ve checked the permissions on the folders and they seem all good. Besides that everything was working well before changing the php.ini. In the meanwhile I’ve deleted the php.ini and the settings are back to default. Still not running.

Attached a screenshot

What are the permissions of files and folder and what about file/folder ownership. The error message clearly states that the session file cannot be created, so the webserver user is not able to write this file.