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This article explains why only one ChannelLinkUpdated event is returned when using a Channel Listener.
Customers with one or more published channels containing multiple entities within a Channel node may notice that only one ChannelLinkUpdated event is returned, for example, when changing the index order of an entity in Plan & Release by dragging and dropping entities in a list.
Why isn't an event thrown for each entity changing its index?
Throwing one event for each reindexed entity isn't possible, since there can be thousands of entites changing their index at the same time. Returning an event for each changed entity would flood the system and slow down performance. That is why only one ChannelLinkUpdated event is thrown.
If there is a need to show all changes you need to handle this in your extension.