ION - SOME fixtures have stopped changing colours

Hey all, there have been a number of students using our ION to program their plays. Now a number of LED fixture (lustr2 / F945FC etc) are not changing colours at all, or are not changing to full saturation, while other fixtures of the same type are working normally. The fixtures are displaying the colour changes on the ML control and magic sheets, but not in the theatre. I've tried using different show files, and creating a new one from scratch - no change. Any ideas would be appreciated.. 

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