Till its FaQed the interpretation is that each mindshackle scarab causes its effect independently. If even one hits then the model can not attack that round, however for each failed check the model does d3 attacks to its unit or its self. Any other interpretation steps beyond the limited amount of info given in the BRB and the codex.
That would be your
interpretation, not the
interpretation.. big difference.
I think I would reverse my position having reread the rule: you can be made to take multiple tests for MSS... but you will still only do D3 attacks onto your unit. My reasoning is that the MSS rules say that the randonly selected base contact model must immediately test or suffer _____: there is nothing stopping them being made to test multiple times (although I would hope and FAQ would). However, the D3 attacks are in place of your attacks... and you only get 1 set of attacks, so you can only make D3 attacks no matter how many times the fail the test.