Q2015 R8 - password file corruption

I take it that if we do NOT use the cloud / mobile sync, then we are OK. True?

That's what I gather, and that has been my experience.

However, I would check your backup parameters. Some time after R7 was installed on my Quicken I noticed that I was no longer being invited to make manual backups; investigating I saw that the backup options had been reset to defaults somehow. I can only conclude that either R6 or R7 was to blame. A couple of other, less important, options seemed to have been set back to defaults in the same time frame, but for it to quietly stop doing backups seems rather serious to me.