There are two problems.
Firstly, you’re not using the Notation Bank of GPO instruments. (which are all prefixed by n- , e.g. n-Viola KS.)
The Notation bank and the Standard bank (which is for live playing) have the key switches in different octaves.
Secondly: in the GPO Strings Expression Map, you have Pizzicato set to F2. It should be F-2. (Compare to all the other switches in the map.) But obviously, the C-2 to F-2 range only work for the Notation bank, not the Standard bank of instruments!
You can audibly hear the additional note, because it’s in the viola’s range!
You’re also loading an unused Violin 2 sample into slot 2 of every VST instance, which does nothing but use a little bit of time and memory.
If you use the GPO5 template from this page, you shouldn’t have any of these problems. Or, better yet: use my latest template, though as you’re on Windows, you’ll need to install the Sforzando VST to gain the latest ARIA update.