Sounds like the platinum findings might have been soldered with low
grade white gold solder.
I had a recent experience where I was presented with a plat
engagement ring with baguettes, I was to tighten a baguette. At the
first touch of the tool the white gold solder just gave up the ghost.
The break was jagged and spongy looking. The jeweler who did it
apparently had rhodiumed so the gold didn't show. I told the customer
I could fix it properly but he was insistent on bringing it back to
place of purchase. later i was told that jeweler said, upon hearing
my observation about low white gold solder on platinum, "There's
only one kind of solder for jewelry".
Maybe it was the same guy?
Gosh I hope there aren't two of those walking around.