Used Scribus 1.5.3 & 4 on a Windows 10 64 bit machine and seems to work OK.
As far as I can tell, the reasons I have trouble getting resultant pdfs past the Lightning Source quality control bods is either something I am doing wrong or because I've "still got something going on with either your program or machine, it's rare that they" -(the tech bods)- "have crashes like this so you might want to look into delete/reload your program or something" is what they told me.