Extension is not ringing in ringgroup but is ringing when dialed as an extension

i have an extension with number 101. this is a fritz!fon sip phone. when i configure an incoming route to use extension 101 it works. phone is ringing.
when i put 101 in ringgroup and configure the incoming route to use ringgroup 500. the phone is not ringing and asterisk says the phone is busy/congested.
when i put another phone in the ringgroup, for example 100. this phone rings (not a fritz!fon) but only the 100 and not 101. (of course using the ringall setting)
i thought is was a bug, so i filed a complete bug report, but this is closed because asterisk is using the same dialing patterns. so not a bug.


so perhaps it is the extension config. can someone help me out?

freepbx distro 7 rc1

It sounds like an issue with the phone’s firmware to me; I would try taking it up with the manufacturer.

Updated freepbx to latest version. Ringgroup is working again with both extensions.