What I can understand though no expert ..the eligibility was recommended pass at end of Mar 2017 by Case Analyst. So when the file moved to case officer he changed the status as wanted to review some aspect of your case so it changed back eligibility to Not Started. As your security screening is ongoing the eligibility status didn't change and would change back to passed once security review is completed.
Though you will have more detailed explanation in the end of notes whether there was any specific reason for the eligibility change (if it has not been redacted)
I hope it is all sorted out soon!
thank you rg74. your message votes for what I proposed initially. and I guess the op here needs faith more than our soothing technical consolations. but then faith we can't give to each other. and isn't it getting eroded step by step starting with the thought that my country is not good enough, my friends and society not enough.....and then I put my future in hands of a remote promise of a "better" income, society,job an what not. and as I get each of these in varying measures I may find losing something else inside me...faith.... which has till now given me the option to fail with grace