I would say putting yourself in a position of losing your bounty (which is indicative of having a lead) is something worth discussing.
If you make yourself prone, then it's a sign that perhaps you weren't positioning well at one point in match. Then perhaps you don't deserve the S rank.
That's not to say just because you died ONCE means you're not worth of S rank but how consistent are you in preventing that mishap from happening? If you have never net a kill or objective since the last death and died again then it's saying that in that moment you weren't being proactive at the time you were given another life. So because you didn't do anything meaningful with that life you lose out some point upon getting your ranking.
This is all very dynamic but it's something to think about next time you go 'super positive' in your KDA. When the match is over, did you still have a bounty on your head? Then when you get your rank, what was it?