So, I'm having the issue with playback. It seems that staves are piggybacking off of the staves directly below them for playback. The "audition" of the sound is spot on. The problem arises when you actually play the score, whether it's just the instrument solo taco or with others plying.
This is a brand new issue. I'm experiencing this on scores I've been working on for a few weeks with no problem. Like my ex-wife, it just went nuts. It just seemed to happen out of nowhere.
As an example, if I have an Auxillary Percussion line set up with a electric bass part underneath of it-the note input will be super-duper. When I click the individual note head, the auditioned sound is perfect....but then the playback now turns a cymbal roll into a bass slide. (fraking bass players, right?) I've moved the staff to different spots on the score. This "crosstalk" happens wherever I move it. To whichever instrument is below it.
I am on a serious time crunch since I burned about 3.5 hours trying to sort this out yesterday.
Do you have enough instances of VDL (Kontakt Player) in your Playback Device to handle the number of instruments there are in the score? Add one more instance and see what that does.
If I saw correctly from the Tapspace forum topic you started, you've deduced that the issue lies within the auto-loading bug that showed up in Sibelius 7.1.2. Since the exact behavior of this has not been consistent from user to user, we as individuals are left to find our own workarounds until Sibelius is able to release an update which has it fixed.