So first of all you need the Audio Assistant from the Galaxy Store
This is what i did:
-Activate Bluetooth and connect your bluetooth earbuds/headphone
-Launch Cubasis and load a project
-Play the audio
-Push volume up or down so the volume bar on the side of your screen pops up
-swipe from the volume bar towards the middle so it folds out to the Audio Assistant pop up panel or push the Audio Assistant bubble to bring up the AA pop up [depending on how you’ve setted it up]
-on the left of the AA panel you see a slider with the cubasis icon
-above that slider is a circle button, which allows you to select the output (speakers/bluetooth)
-cycle thru the options untill you are back on bluetooth (tapping the button will cycle to the next option)
Once back on bluetooth you should hear cubasis’s audio thru your bluetooth buds/headphones
Your AA pop up panel might have different colors because i skinned mine
Hopefully it resolves the bluetooth issues you have as it did for me.