Can't update plugins thru adminpanel

[Steffen Buschkemper]

Hello Mike,

@first thanks for your help.
I have tested your solution and the problem persists.

I'm pretty clueless.
Firewall is not the problem.
Folder permissions not the problem.
Curl is used.
Actually, all server settings are the same as in 4.1.

I have only changed files that you have offered here, because of the login issue in 4.2 (Session Problem). -> Here
Plugins can not cause this trouble, because no installed.

Best regards
Steffen