Perhaps the problem is that you’ve got inappropriate expression maps chosen for the player now? If you click the cog icon next to the ARIA Player in the VST Instruments rack, you’ll see a window that shows which expression map is being used for each channel. It might be that you should be using no expression map at all, since Dorico doesn’t come with any expression maps appropriate for use with any of the libraries compatible with the ARIA Player, so it might well be that the expression map in use is sending a controller that’s changing a setting in ARIA unexpectedly.
Also, do make sure that you are using the “multi” (i.e. multi-output) version of the ARIA Player, so that each channel in ARIA is routed to a separate fader in Dorico’s Mixer.