I have made about 50 bamboo backed bows with urac and at least that many billet splices with no failures. I love being able to make a heat correction on a urac glued blank without it coming apart.
You are probably correct, some part of your gluing process is flawed. If Urac fails for you on wood bows, what ever else you use may fall as well.
I suspect you are degreasing your osage with something that is staying in the wood and causing failures.
I don't degrease, I found it a waste of time and unnecessary, another bow making "old wives tale".
I rough up the surfaces with a toothing plane iron and glue up my backings or splices, no failures.