Freepbx through VPN

Im using Freepbx: PBX Firmware: 6.12.65-32

i have around more then 50 ext, in diferent vlan , , and working fine.

Lately i have added 10 extra extension through a vpn.

and with first implemention they were working fine all of them, now if i have power issue, when the mikrotik where vpn is established is down then maybe some others ext will be okay and those 3 wont be …

But mostly are not working, is there anything i could do … or change.