I think I have found the problem which is causing the I/O issue in FL studio.
in the Vst. DAW Settings.
1. go to Preferences
2. go to DAW settings
3. select the last item "Send MIDI Data to Embedded Synth" and
select "enable".(This should really be the default. Me think!...)
4. select OK
this should fix the I/O issue.
You should be able to hear all the tracks playing as they should
I cannot say if this will work with other DAWs but, no harm giving it a try.