I don’t know if this is the reason, but I’ve found that once you build the plugin for the first time, then Logic (at least) won’t let me change the IO configuration
So for example, if I build with this config:
#define PLUG_CHANNEL_IO “1-1”
and then change it to:
#define PLUG_CHANNEL_IO “1-1 2-2”
the changes will not take effect.
Any other changes do work though.