Michael,
in the meantime I have a reply from my hosting provider: They didn’t find any errors in their server configuration.
I checked my php_error.log and found no entries.
I ran your “test script version 4” and – as far as I can judge it – everything seems to be fine. I have sent you a screenshot of the results of your test script by email.
If you want me to run a different script I’ll do so of you provide me with it.
Thank you