I created a loop in LoopMash, then exported > Audio Mixdown > selected Mix Out (by mistake, should have been LoopMash), and then imported it into the project. Later decided I didn’t want the loop, deleted the LoopMash track and all traces of it… but when I reopened the file, the loop I deleted is playing… and it’s coming out of the Mix Out channel. So there’s no instance of LoopMash, just the loop I had gotten rid of - I thought. Any clue, I figure I’m just missing something easy.
Umm… You said you imported the mixdown back into the project, right? So you’re probably hearing the audio track with the mixdown still containing the loop playing. Delete or mute the mixdown, and the loop should be gone too… 
Try to Solo all tracks one-by-one. You will find, on which track do you have the loop. Meters of Mixer can helps too.