not a bug, after you start an arc you have to trigger certain events by being at the right places at the correct times / in the correct order. I don't know how many you've triggered / which exactly you need ( I only played the arc once till now, planning to replay it the weekend, can prolly help you more then), but the places you should check frequently are: Science Club (duh.), Library, Park and I think (although I can't recall a special event triggering from there besides the date(s)) the Science Exhibition. Hope this mess of a text helped you a bit