BOSH apache http-bind errors

Hello Community,
I have a problem with http-bind. I configured ejabberd and apache2 for unse BOSH thru http-bind proxy, and it works, but not in every case. Test the url is successfull, and bind from a site (e.g. Friendica jappix Plugin) is allways successfull. But binding from localhost has a strange behaviour. Sometimes it works and somtimes I have a "client denied by server configuartion" in the apache error log:
[error] [client xxx.xxx.xxx.xxx] client denied by server configuration: proxy:http://sub.domain.tld:5280/http-bind, referer: https://tld.domain.tld/webapp/index.php

I've not changed the config of apache or ejabberd, it was just another day.
The bind that fails sometimes is from plugins in Zarafa and owncloud. Bindung from Jabber Clients like, Pidgin works, from outside my lan.
From localhost i cannot test.

Can anybody explain this?

Greetings from Thüringen Germany,
Daniel
I'm Sorry for bad english.