Now you select 'split mono tracks' which creates a left image of your stereo track, and a right one. you'll find that in the 'process' menu I believe. is to bounce that track to another track. So the next step I would do, instead of pressing the interleave-button and switching your complette fx-bin to mono. so you get what you want but the signal somehow will degrade. The problem with this is that you probably have only noise on the right channel, and that will be mixed to the left channel too. Just look for 'mono' there should only be one entry anyway. and select something like 'process to mono'. The easiest, fastest and dirtiest way out of this is to right click the clip of that track. You probably have recorded to a stereo track as others have said too.
