Constant disconnect on XMPP server over HTTP proxy

[forwebonly at web.de]

Hello,
ist there some way to make XMPP connections over a HTTP proxy less prone to disconnects?
I regulary get disconnected - every some minutes ...

My setting is as follows:

SSL/TLS
Port 5222
File transfer proxy is set

Proxy-settings:

HTTP
Host is set
Port 8080

Is there something i could change to get better results?
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