audio maxes out and distorts

Audacity 2.3.2. Mac Mojave 10.14.5.

New to Audacity.
I’m not sure what its called but when recording through audacity the audio maxes out and distorts (see attached pic).
Ever since I have tried to use this program with new Mac it continually does it at random times. Never had this problem with Windows.

I’m recording directly from my djm900 nexus using the cord with a usb b - thunderbolt connections. On the Mixer I keep the levels at 0db for both channels and the audacity recording metering toolbar at -18.
Why and how do I fix this?
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Screen Shot 2019-06-18 at 4.00.38 pm.jpg