There is no “expression map for Pianoteq.” It works fine using the Dorico “default” map.
It plays back Leo’s example OK for me. I tried adding some repeats bars and a rit at the end to match the original problem, but everything still worked.
However you can reconfigure just about every MIDI command that Pianoteq responds to within Pianoteq itself, so just from the demo video there could be any number of “hidden” reasons why this doesn’t work correctly.
Also the video appears to be an overlay of two different screen grabs, and it doesn’t have any sound when I view it, so the Dorico and Pianoteq parts of the video could be out of sync as well.
I use Pianoteq a lot, so I would be pretty surprised if there was a fundamental problem like “pedalling doesn’t work” and I hadn’t noticed yet.
Note, by default Pianoteq listens to all MIDI channels, so if Shiki is trying to play a written part AND chords on the same instance of Pianoteq, that might well create chaos (just as it would on a real piano!) In that case the solution is run two copies of the Pianoteq VST and configure them to be selective about what MIDI channels they respond to.
The default playback configuration in the Mixer DOES send both chords and written notes to the same channel, but needing to change that is hardly a “bug” IMO.