Strange playback behaviour

I’ve got a strings quartet set up in Dorico 5, which each of the 4 instruments assigned to a different midi channel. What is strange is that when I set to solo (“S”) one of instruments 2 to 4, I do not hear anything, whereas when I set to solo the first intrument, I hear all of the 4 instruments playing.
I use PLAY VST engine from EW and each of the instruments is assigned to the correct midi channel.
Any idea how to solve this ?
Thanks

Welcome to the forum, Marc. My guess is that you need to configure each channel in the EW Play interface to be returned on a different output. It sounds as if all channels are returning on the first output from the plug-in.

Thanks @dspreadbury , it solved the problem !