volume error using buses

Hi all,

I'm using MainStage live with the playback plug for each of my backing tracks.

I'm experiencing a 10db volume increase for 2 seconds every time I start any song in my manistage 3.2.1 set.

I have all my keyboards routed to one stereo bus say Bus 10 with a compressor on it

All my drum tracks routed to another say bus 11

I don't get the spike if I just select the default output 1 / 2 for each track.

I believe the issue is because I am using bus groups for my instruments I have checked my playback .wav files and they're good.

What gives, is anyone else having this issue?

This was happening on MainStage 3 also.

Thanks

osx 10.9.5

MainStage 3.2.1