Found a bug with deck keyboard mapping... it seems that in deck mode if I map a set of keys to trigger clips - when I trigger the clips rapidly the new clips alpha is set at 0 / off ie: it is blacked out... even though the layer opacity slider is fully on .... a quick wiggle of the layer opacity slider brings back the clip.
I also managed to make the software bomb completely using rapid key changes to trigger clips - but I actually think this is related to some of the files sizes of my content ... ie 6Gb+ ... I will check it again with some short optimised clips ...