I am periodically having a problem with some communication function Blocks on switch-over in an M580 hot standby system. What can be a possible reason?

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Issue
Having a problem with some communication function Blocks on switch-over in an M580 hot standby system.

Product Line
EcoStruxure Control Expert (former Unity Pro), Modicon M580

Environment
Unity Pro v12.0, BMEH586040

Resolution
In a Hot Standby system, it is important that the variables in the communications blocks are not transferred from the primary to the standby so that on a switchover the blocks will not be is a strange state. Therefor all variables associated with the blocks must have as an attribute that they are not exchanged. So the check box for EXCH On Standby MUST be unchecked. See the screenshot in the attachment.