UpdateInstanceTransform with a rotation causes instances to jitter/skip frames when scaling animation speed

I have a weird bug where changing the rotation of my instances is messing with the the scale (I think)

I have a HISM’s vertex animation set up where the Instance scale changes the animation speed:

Here I have the code updating the instances position and scale (but not rotation). And for testing purposes I’m simply scaling each one up a little bit:

This works fine. You can see in this video, everything is smooth and the smaller ones move slower than the larger ones, which is the intention:

https://streamable.com/gn7sc

However I get a problem when I update the FTransform’s rotation in code. In this code all I am doing is rotating the instances a bit more every frame:

What happens is that it starts off fine, but after a while it seems like the animations are skipping frames or something like this, and looks terrible in game. This ONLY HAPPENS WHEN UPDATING THE ROTATION:

https://streamable.com/ogvfr

So I’m not exactly sure what the issue is. Changing the rotation doesnt seem to affect the time because if I run it with rotations but without scaling the animation speed by the instance scale it works fine, just everything is the same speed: https://streamable.com/f9qsn

I think maybe the scale given to the material is being affected by the rotation somehow. However I would have thought if the scale was incorrect then the instanced meshes would be changing size, which they’re not.

Edit: this seems to be a problem at 2000 instances. When I changed to 1000 instances, it stopped being an issue, not sure whats going on because at 2000 the frame rate is 80, and at 1000 its over 120 so its not really lagging anyway.

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Thanks