It would appear your third variable is the glue, even if silver
compatible, it maybe in conjunction with the leather other by
products are created. also, you didn't mention what tonnage the
leather is, the two basic are either organic vegetable (oak) or
smoked, the second being chrome tanned (or other metallic salts).
actually every tannery has several unique formulas for their
leathers, so leather from two companies maybe called the same but
with different additives that could be reactive catalysts.
Your best bet would try a different leather source, then retry your
test with a variety of adhesives.
Warning: "Craft Store" leathers may have the same packaging, but
multiple tanners, plus each color is a different "brew" of
Sorry I'm unavoidably vague, but I've been out of leather craft
quite a while!
Have fun, Ed