If the installation is not working as expected when a 2N intercom is integrated to Loxone, and you are confident you have followed all the steps found on the wiki.2n.cz site for the version of miniserver that you are using, then change the sip service you have setup with if you have followed the example from the wiki site

the example shows the use of antisip service, however we have seen some circumstances when this does not work well (seems to be when calls are going to certain service providers mobiles - EE for instance)

changing to iptel service for the SIP setup has resolved the issue for several installers projects