Excessive switchovers can be caused by unstable network elements. Events causing instability should be dampened at the source (ports may support event dampening). Event dampening control is not configurable under NAT. However, a dampening mechanism is built into stateful inter-chassis NAT redundancy by not allowing a switchover while synchronization is in progress.
Considering that a full re-synchronization is triggered after every switchover, the next switchover can occur only after the amount of time needed for full synchronization of flows. The new standby starts deleting flows and after this is completed, all flows from the newly active ISA are copied over to the standby.