Actually I've just gone back to the project that was a problem, and the problem was still there. My other projects don't exhibit this issue. However, I can't export this project with any combination of buffer/MIR latency setting, unless I do it in real time. Unfortunately I can't do it in real time, because some of the plugs are causing glitches. So I'm going to have to export stems as 32bit float, MIR instruments in real time and then combine them, with the Master Bus processing for a final export.
This is not a good way to work, and if I can't figure it out, then MIR is not going to be part of my set-up, unfortunately.
Martin, could this be anything to do with the fact that I'm using the audio input feature of MIR?
DG