pfSense multi site-to-site vpn with openvpn

pfSense multi site-to-site vpn with openvpn

I've a strange behavior of the pfSense system when establishing a multiple
site-to-site connection. All sites use the same version of pfSense (2.1).
I've three sites which are all in different subnets.
Sites and subnets:
Site A: 10.1.0.0/16
Site B: 192.168.0.0/16
Site C: 10.3.0.0/16
Linking sites:
Site A (Server) < 10.10.10.0/24 > Site B (Client)
Site A (Server) < 10.10.11.0/24 > Site C (Client)
Site B (Server) < 10.10.12.0/24 > Site C (Client)
All sites need to be connected directly. I've managed to set this up
without a problem. All sites were connected and I was reaching the
different networks from each site. However, the connections are unstable.
When I remove all configurations for site C the connection between A and B
works perfectly. As soon as I enable the connection with site C, A-B will
be unstable (PING works randomly).
Is there a limit of setting up active site-to-site connections with
OpenVPN in pfSense? Any suggestions for other configurations?
Thanks, Sead