Your ARIA plug-ins are incompatible with mine – probably you’re still using VST2 on Windows – so I’ve have to replace your “Strings” VST with a fresh ARIA vst instance, and load the GIFF instruments, and add the Expression Maps.
After doing that, I have been able to reproduce the problem, but I have also not been able to reproduce it, and I don’t know why. I’ve tried resetting the Playback Options, which I thought worked, but I’ve also been also to get it working without doing that.
Here’s a list of things that needs addressing, but I haven’t identified them as the actual cause:
First of all, you’ve set all those ARIA instruments to go out on the same channel pair, so they will only appear on one Dorico mixer slider. Where it says “1/2”, click on that, and set each instrument to a different output pair – e.g. 3/4, 5/6, 7/8, etc. (Otherwise, there’s no point in using the “Multi-output” VST…!)
Your expression map uses C-1 for the “Natural” expression, when it should be C-2; so it’s not switching back to Natural. (Perhaps try changing the expressions on a passage of notes between Arco, Pizzicato and Tremolo, and seeing if that’s better.)
You’re also using the same Violin sample for the 2nds as for the 1sts, and there is a Violins 2 KS instrument. (Which in fact has several more articulations, because they accidentally copied over the GPO5 instrument without restricting it!)
One other problem is that you’re using Single Players (in Setup mode), rather than Section Players. Ideally, you’ll want your Playback Template to distinguish between the two, so you can use the appropriate sample instruments for Solo and Section.