The following two scenarios are not protected by the Diameter multi-chassis redundancy:
Loss of the intra-peering (MCS) link. This scenario causes a split-brain scenario where both nodes act as stand-alone nodes and they both try to open peering connections to the Diameter servers.
SRRP Active-Active state, where the SRRP messaging path between the two SR nodes is broken and consequently, both SR nodes own the Diameter application session (for example, Gx session).
These two scenarios do not meet the minimum requirements (MCS and SRRP must be operational) for successful Diameter multi-chassis operation, and therefore, are not supported. However, after the valid control channel states are restored (intra-chassis link is restored or SRRP states become stable, Active or Standby), the expectation is that the redundant system brings itself up to a valid protecting state.