Failover mechanism in fxbais (Schneider-Electric PI interface for Windows) doesn't lead to a failover when the primary interface node loses connection to the network (f.i. when its NIC fails). It just starts buffering and sends its data after the connection is back again.
It keeps on updating its watchdog CALC block on IA, so no take over is initiated.
Some applications require "near real time" data, so if it comes in a day later, it's not very useful.
In such a case, the secondary interface node could perfectly take over the data collection.