Okay.
But do note: I'm specifically talking about slot image keys. Other types of keys don't seem to be having problems as far as I can tell.
I also realized that clicking on a slot image key really doesn't select it in the normal case. Clicking on the key selects the image or slot in the tree and in the viewport but it doesn't select the key I was clicking on in the dopesheet. Still kinda weird. It's normal behavior ("normal" meaning that's how it's working right now without errors) but I'm not sure if it's intended behavior.
Still, possibly related to the crashing.
To reiterate what Spine Editor currently does: A single click on a slot image key won't select that key in the dopesheet. Dragging that key to move it does end up selecting it though.
My error (which happens repeatedly but not always) is that when I delete an image slot key, the key "persists"— ie, the yellow box is still there. But clicking on that remaining key crashes the program.
It's obviously not a case of two keys really close together. If that were the case, dragging the key would've moved one key, and left the other behind.
Moving the key didn't clear out the bad state. It's still in my file. When I try to select it, Spine crashes.
Another thing about it was that these image slot keys were copied from another animation. (because I was using separate animations to save alignments and setups of specific body parts at different angles, then just copying its transforms into the actual animation clips I'll use in-game.)
