[BUG] Instanced Static Mesh: New instances visually replace old instances after instance removal

While dynamically adding and removing instances to an Instanced Static Mesh, occasionally instances will disappear after adding new instances. These instances are not removed, but are made invisible.

To Reproduce:
In a blank project create a new actor that contains an Instanced Static Mesh component that is populated with instances during construction.

Add an event that removes instances from the component.

As well as an event that adds new instances to the component.

Run the game and ress the H key, removing the specified instances, as expected.

Press the J Key, adding the new instances as expected, but unexpectedly hiding other instances in the Instanced Static Mesh Component.

Checking the details panel for this example shows that there are 70 instances, as there should be. +100 from construction script, -50 from the H Key event, and +20 from the J Key event, however only 50 can be seen. Furthermore the missing 20 have no moved at all, and if their position is manually updated in the detail panel they will reappear.

Current Workaround: Clearing all of the instances and then creating new instances in their place will result in all of the new instances being visible.

UE-53053 seems to be the same thing and is fixed in 4.19.2.

I will try updating to that version and see if it resolves the issue in the test project.

Hello,

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Thanks