Got a classic strap blowout here. Whenever you put a strap in a seam and don't tie it to an adjacent panel, it's very likely to pull the seam apart eventually, as it's done here:
This bag actually had some bartacks to tie the strap to the back panel. Unfortunately, the seam allowance that the straps are in is very small (1/2") relative to the thickness (it's lined and seam-taped, so there're ten layers at one point) and one bartack completely missed the end of the strap. The bartacks also weren't installed in a way that transferred the load from the strap to the back panel, so the seam failed anyway.
Other contributing factors: The thread is shit, and
there weren't enough stitches per inch. Also, the fabric doesn't have the tightest weave, which helped it fray at the end and pull out of the stitches after the main seam failed.
Took everything mostly apart on the blown strap and resewed it, and reinforced the other strap. This pack is a fully padded camera bag so it was nice to have the post-bed machine. I had started sewing it on a flat-bed, but it got too hard to keep the bag in place.
Finally, sewing the straps to the back panel.