Hate to breath life back into this old gem, but why am I now seeing this behaviour randomly in X2a?? What the?? Both audio and midi clips 'vanish'! Anyone ever get to the bottom of this?

You should ask this question in the x1 x2 forum. It is always best to start a new thread and in the correct version forum wher ethere are more users. , you waste peoples time making them read old posts. Ask you question there and please include information about your system and audio interface as that helps get faster answers,, good luck, sounds like a dandy.