Light function and actor position error

I’m using a texture to drive light flicker in a light function while using the actor position to pick UV coordinates so the light flicker isn’t the same based on position. So for example: if I have multiple torches in a hallway then the lights don’t flicker at the same rate. As of 4.15 I get the error:

(NodeActorPositionWS) Actor Position>Expression only available in the Surface and Deferred Decal material domains.

What is the reason for the block? This feature has worked for years and now its blocked.

I’m trying to avoid creating multiple MICs for this and wanted to maintain a level of randomness. Are there any other ways to achieve this result without?

Thanks in advance.