I’ve had a look at this score and it’s hard for me to see what is and isn’t working as I don’t have this library and the playing technique symbols aren’t shown as expected (I think you can make these available in other projects by pressing ‘Save as Default’ in the Playing Techniques editor).
However, there are a couple of techniques you can use to help diagnose what’s going on. Firstly, in Play Mode press the button to show the Playing Techniques lane. This will show you which switch is used in the expression map, and for how long. For instance I can see that ‘Pluck 1’ applies only to the first note. I don’t know if that’s intentional, but there are two different types of techniques: articulations (which apply only to the note they’re attached to) and directions (which are ‘sticky’ and last until another that resets them). So you can scroll through to find the keyswitches in the expression map that Dorico is inferring at each point. That will help in working out whether the problem is in the playing technique or in the expression map.
Another useful technique is to export the track as MIDI, as this will contain all the keyswitches from the expression map with the same timing that is used in playback. You can then look at this in a DAW to check it’s outputting the switches you expect. Or you can do it in Dorico by adding another instrument, switch to play mode and then just drag and drop the MIDI file to the first bar of the empty instrument. This will then show you the keyswitches so you can compare them to the source instrument.
eg see this:
I suspect though that you might be bumping up against a current limitation in Dorico in that it’s not possible yet to specify mutual exclusion groups in expression maps, so Dorico has no way of knowing whether Pluck 1 and Pluck 2 are additive, or alternative. This is an area we hope to improve in future versions.