External instrument & weird levels..?

I've been starting to use the OP-1 with Logic for some more editing abilities.
However I've been running into a weird problem. I connect the OP-1 as an External Instrument on a midi track, then I've sent it through a bus to an aux track to bounce the recordings when I'm done editing the midi. Here's the weird thing though: As soon as I connect the track to a bus, the signal played back from the OP1 is suddenly much stronger which makes it peak hard in the output. It doesn't affect the aux track, but only the output track (see attached image).

What am I missing here? Not very familiar with Logic so I'm sure the problem lies with the user, not the program...

Thanks in advance.

(I realize I might be on the edge of what this forum is made for, but since it's for using the OP-1, even though the problem lies with the daw, I hope I fall on the right side of the line. Also there seems to be a lot of nice and smart people here that might know why this happens.)

both the track and aux are going to the output maybe. disable the track to output so it only goes to the aux.