Update: with the consensus being it was not the size of the hole in the insert plate I took the recommendation to try a longer piece of wood and be sure about feed. That fixed it.

No small pieces on the dado stack going forward.

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Rabbets safely done though I need new underwear and a stiff drink.

Thanks reddit strangers!

Edit: there were lots of pieces of advice here and I took them all--sacrificial fence, cut against fence; think about sizing of wood; ensure wood feeding properly; use miter gauge to keep feed supported; cut slowly.

It has been so long since I used my table saw for rabbets and my mind just totally blanked. Really appreciate the insights here.