I checked the attic when I first noticed the problem and didn't see
any evidence of a leak: no stains on the sheetrock or anything like that.
And since humidity is not really an issue here, I'm going to say, no, I
don't thing it's a moisture problem...

Well then, (if the ceiling is falling in patches) you are dealing with an
improper installation and subsequent failure of the texture material which
will have to be removed. I fail to see how an oil-based primer will
penetrate through the latex paint and then through the texture material and
then bond to the paper coating on the dry wall. Good luck!