we upgraded from GW 2012 to 2014

Our system:
- primary Domain with 4 post offices on a 2-server-cluster, OES 11 SP2
- 2 secondary domains with a GWIA each on two SLES 11 SP3 VMs

Now every few hours the one or other MTA becomes unresponsive; as far as I
can tell the agent keeps running (it shows even "Normal" in GW Monitor and
rcgrpwise status) but I can't access its HTTP Console and Admin Console
shows "grey" (not red). Sometimes when I restarted one MTA another became
unresponsive. In addidion to that today we had both GWIA down - in this case
really down, "red". Only the POAs seem to run stable.

And, even worse, since today, GroupWise Monitor stopped to work. Crashed on
one cluster node, "Segmentation fault" whenever I try to restart it.
Migrated to the other cluster node, run a few hours, "Segmentation fault"

Any ideas what's going wrong?