Web Proxy / Allowed Service not working

Hello,

I have a problem with the "transparent proxy" and an additional service.
In webfiltering I use the "transparent mode", with HTTPS-scan.
No full transparent and no authentication.
I have no url-filtering categories or similar.
In "advanced" I added the port 8444, which I need, and press "apply".
But I'm not allowed to use this target service.
But in firewall-log I get always the following entries

14:51:40Default DROPTCP172.16.100.7:54733→212.117.203.111:8444[SYN]len=48ttl=127tos=0x00srcmac=0:c:29:33:25:64dstmac= 0:1a:8c:12:a4:90

In the webbrowser it is the url: https://my.sipcall.ch:8444

Why does the webproxy not support the added service on port 8444?

Astaro is 8.306

regards
Martin