This issue is most likely to happen due to incorrect irrelevant firewall/network settings.
Please, check the firewall settings (Which IPs should I whitelist in my firewall?) to make sure they correspond with our recommendations.
Additionally, in case the problem relates toaffects Gigaset handset devices, the Gigaset handset device settings should be checked. Absence of a proper DECT signal for a handset can also cause SIP messages not being answered at all times.
For verification you can make a call to a Huntgroup containing only DECT handsets and compare the results with a call to a Huntgroup containing only Fixed devices. If the issue appears in both scenarios, the firewall/network settings should be checked.
Please note that in some cases the switch can also be the cause of the issue. Feel free to use our extra tool VoIP Connection Analyzer to check on the local network.