Thank you for helping me to understand what's going on here.
My guess is that whoever made the riser/frame unit (Forest River? The axle manufacturer Dexter?) ran short of the proper material and grabbed something out of the stock pile that had a cut made between the places the bolts are fastened, leading to 2 tabs sticking down rather than a single complete bar. That's my guess.
Both sides failed, the right side first, then the left, but I haven't gotten underneath to see if the left side also has metal missing. I figure it must, tho.
Frankly I am bewildered by the axle guy's comment that the axle isn't bent, but to me that is not very important right now. I just want to be road-worthy.
Again, thank you for helping me to understand this whole thing.