they are likley issue and limitation on the various s/w (openocd, stlink driver etc ...) when you have mtulipe instance of the same usb -device . certainly they operate on the first device they found and we have no way to change that at the moment like givin the serial number that would ne a nice feature.
Regarding debug wihtout flashing that is like “debug attach to a running target/process”,
but i think that type of debugging is not suported at the moment by the plugins,
how you can do that take an ac6 debug configruation, duplicate it , rename to smthg like “xx no load”
go in the debug configuration startup pane , uncheck the “laod image”. voila..
Of oourse if you use that config and the loaded binary doesn’t match .elf image nothing gonna match (not even initial break at main)