Regards knowing what rule was "judged" to be broken, there is a rule number posted below the clock and beside the penalty duration count down, as per this photo: www.www.dropbox.com/s/jegvur0kvnhuawa/R15.JPG?dl=0 . Has this now disappeared? (Play on iOS and haven't noticed if now removed?)
I have had P/S penalties off the start line twice, before and during the worlds qualifiers, so I don't think this is a new bug.
Rules engine bugs is the big topic. Sailx spent years refining theirs and it was still imperfect. The developers could consider telling the non-penalised boat what rule was judged to be infringed, and give the option of transferring the penalty if they deem it to be unfair/incorrect. But there is less of a community here, and no replays/fair play spirit/rules awareness here compared to sailx so I don't think many would feel compelled to transfer penalties.