I have had similar issues with both iMini and Galileo organ running in IAA. When creating a mix down or audio freeze the IAA tracks seemed slowed down.
Sometimes a restart would temporarily fix the issue, sometimes not.
I think I have tracked it down to being the hardware buffer size, and somehow this is being affected by the settings in audiobus even though audio bus is no longer used once I have recorded an audio track with it. Once i match audiobus and cubasis buffer size, the freeze and mixdown works ok. I am keeping my eye on this to see if my findings are constant or as variable as the results I get when restarting.