(Windows) Client (2.2.2) can't connect to status.php

Hi there. I have set up an owncloud server and everything works fine now except the client. When I put the URL into the client, it says that it couldn't connect to "https://[...]/owncloud/status.php"

I have done some research and read many other entries in different forums, but none of those seemed to fit to my case and none of the suggestions worked for me.

So here are some informations:
status.php
When I open the URL of the status.php in the browser, I get:
{"installed":true,"maintenance":false,"version":"8.2.7.1","versionstring":"8.2.7","edition":""}
which is the correct output, I think.

Client log
The logfile of the client reads as follows:
07-28 16:50:47:078 0x61e028 OCC::ownCloudGui::slotOpenSettingsDialog: No configured folders yet, starting setup wizard
07-28 16:50:47:655 0x61e028 unknown: QIODevice::read: device not open
07-28 16:50:47:655 0x61e028 OCC::OwncloudWizard::slotCurrentPageChanged: Current Wizard page changed to 0
07-28 16:50:47:655 0x61e028 unknown: Failed to resolve EGL function eglGetPlatformDisplayEXT (Die angegebene Prozedur wurde nicht gefunden.)
07-28 16:50:47:655 0x61e028 unknown: static QWindowsEGLStaticContext* QWindowsEGLStaticContext::create(): Could not initialize EGL display: error 0x3001

07-28 16:50:47:655 0x61e028 unknown: static QWindowsEGLStaticContext* QWindowsEGLStaticContext::create(): When using ANGLE, check if d3dcompiler_4x.dll is available
07-28 16:50:47:765 0x61e028 OCC::SocketApi::slotNewConnection: SocketApi: New connection QLocalSocket(0x6a92410)
07-28 16:50:50:078 0x61e028 OCC::OCUpdater::backgroundCheckForUpdate: virtual void OCC::OCUpdater::backgroundCheckForUpdate() checking for available update
07-28 16:50:50:686 0x61e028 OCC::NSISUpdater::versionInfoArrived: Client is on latest version!
07-28 16:51:04:197 0x61e028 OCC::PostfixLineEdit::setFullText: "https://[...]/owncloud"
07-28 16:51:04:212 0x61e028 unknown: QIODevice::read: device not open
07-28 16:51:04:212 0x61e028 OCC::AbstractNetworkJob::start: !!! OCC::CheckServerJob created for "https://[...]/owncloud" + "status.php" "OCC::OwncloudSetupWizard"
07-28 16:51:04:259 0x73b0740 unknown: ERRORING OTHER QHttpNetworkReply(0x6b26078) QUrl( "https://[...]/owncloud/status.php" )
07-28 16:51:04:259 0x61e028 OCC::AbstractNetworkJob::slotFinished: void OCC::AbstractNetworkJob::slotFinished() 2 "Verbindung beendet" QVariant(Invalid)
07-28 16:51:04:259 0x61e028 OCC::CheckServerJob::finished: error: status.php replied 0 ""
07-28 16:51:04:275 0x61e028 unknown: Failed to resolve EGL function eglGetPlatformDisplayEXT (Die angegebene Prozedur wurde nicht gefunden.)
07-28 16:51:04:275 0x61e028 unknown: static QWindowsEGLStaticContext* QWindowsEGLStaticContext::create(): Could not initialize EGL display: error 0x3001

07-28 16:51:04:275 0x61e028 unknown: static QWindowsEGLStaticContext* QWindowsEGLStaticContext::create(): When using ANGLE, check if d3dcompiler_4x.dll is available
07-28 16:51:04:290 0x61e028 OCC::PostfixLineEdit::setFullText: "https://[...]/owncloud"

There are some error-messages I don't understand, but I think the main problem is the line with "status.php replied 0".

owncloud log
I'm unsure which parts might be relevant. The server is allready in use for some time now, so the log is very long. However, I couldn't find any new entries in the period hte client tried to connect. Any suggestions what I might be looking for?

Client configuration
Client version: 2.2.2 (build 6192) (language: german)
Client operating system: Windows 7 (64bit)

Server configuration
Operating system: linux ubuntu 14.04.4 LTS
Web server: apache
Database: MySQL
PHP version: 5.5
ownCloud version (see ownCloud admin page): 8.2.7.1 (as you could see in the status.php message)
Updated from an older ownCloud or fresh install: updated since 8.2.5, but it didn't work since installation

Special configurations (external storage, external authentication, reverse proxy, server-side-encryption):
There is a firewall that forwards all communication at "https://[...]/owncloud" to the owncloud server. The communication between firewall and owncloud server is encrypted with a self-signed SSL certificate on the owncloud server while the firewall uses a different SSL certificate for external communication.

Any suggestions, hints or requests what extra information I should provide are wellcome.

Do you have HTTP keep-alive enabled in your webserver and firewall? With a timeout of > 60

Hi, this happened to me once and after a while I remembered that I had to clear the owncloud client in the firewall rules as in my setup it was closed by default.
Hope it helps.