I was called to repair a stair tread. I had no idea what to expect. I got to the house and there was a single solid oak tread, 5' long and standard width. It had come apart along a glue joint! As you know, most solid treads are comprised of three or four board widths glue up at the factory then milled smooth, to about 1&1/8" thick. But I have never heard of or seen one come apart. But this one had, right down the middle. So, I pulled it up and took it to my shop (garage) and separated the two halves completely. Then I cleaned up the joint by gently scraping the edges. I then used my biscuit joiner and installed 6 biscuits and re-glued and clamped it up over night. Next day, took it to customer's to re-install with PL Premium Urethane adhesive and a few finish nails. Out of courtesy, I lightly sanded and applied another coat of urethane finish to the tread. It didn't need it but I did it anyway. Just like new again, but better. Just hope the other joints don't come apart.

VERY unusual Gary, its always been my experience that the glue joints (properly done of course) are stronger than the material being glued.
Did the two pieces that separated have opposing grains putting undue stress on the glue joint perhaps?
Anyway, you solved the problem for the client, so all is well.