Long time to render?

You're going about this the wrong way then.

What frame number shows the flicker? What frame number does not?

Render just those two frames and show me.

For purposes of demonstrating shadow problems, you don't need a whole animation, you don't need full size, and you don't need high render settings. You should be able to render two frames of about 400 pixels wide in less than 30 seconds.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)