It’s unclear what you’re saying : I think you mix 3 different things.
- the MIDI track : when you press the “MIDI” button you access the MIDI side of OT, and you can control external gear. This as nothing to do with the audio recording side of OT.
- the Record track, accessed by pushing Fn+Rec button. You will record the source you’ve chosen (A B, A, B, A+B, same for C/D, and/or each internal track / main / cue)
- the Audio track. By using Flex you can play any sample, or the Recording buffer of the Record track.
Now.
What may have happen is that you have set trigs on each Record track to start recording, and when you press play they all start to record (and so erase what has previously been recorded).
If you want to keep your loop for another day, save your buffer as a file. It’s the only way to keep your loop for further use, cause the buffers are erased when you switch off the OT.
If you just want to jam with your Volcas and sample on-the-fly, then use for instance A for the Beats > track 1, B for the Bass > track 2 and C for the Keys > track 3.
You could also record everything from the same A/B input (for instance if the 3 Volcas are plugged on a mixer which output the mix to the OT) : in this config, you would have to arm only the track that you want to record to ensure that you don’t erase the recordings on the other track.
I hope I have answered your question in a way that is understandable 
