I’m happy to hear all thoughts on my first (and not last) failure. This is my 6th bow. I’ve made 4 similar and very shootable flat bows like it. But this one broke after about 20 shots. Just as I was about to get a picture at full draw. 
I had been working on a series of three bows made of ash that I cut 2 years ago. All 3 need backing because of minor bug damage to the back. Very early ash borer damage. They get steamed to reduce prop twist and give them a bit of back set. But, of course I have been losing that during tillering. So I was playing with heat treating to reduce set and increase speed. The first one I heated once after floor tillering and before backing. The one that broke, I’d heated twice. Once after floor tillering and again as I approached final tillering. 
I believe I worked too fast. The tiller looked great. But the fact that I didn’t even stop to take a picture before taking it off the tillering tree to shoot it, is a lesson I think.
Here’s a list of what I think I did wrong. 
I didn’t wait long enough between steaming and heat treating steps to allow the wood to regain moisture. 
I sanded the back of the bow with 80 grit to knock off some small dust filled glue rough spots and pencil marks that wouldn’t erase, and potentially took off material where it shouldn’t have come off. Then I didn’t score it to help the backing stick. 
I tillered too fast. I didn’t work the limbs enough while tillering. And I feel like final tiller came too quick. It didn’t seem to me that I was taking a lot of material off, and yet I got to my target draw quicker and at a lower poundage than on the previous 5 bows I’ve made. 
I feel like I became too confident. 

Too much confidence?