I too had this issue at student housing after the bar shuts .... The future generation eh ? So here's the thing , overloading of a car or people jumping up and down ..absolutely is misuse and should be chargeable but the question is why if you have re elevators does it only happen on one ? Or is it say twenty different buildings covering 22 elevators ? It is relatively easy for your service provider to do an overspeed governor test to see what speed it trips at and seeing as you have bought 22 elevators from them they should have no problem doing this with you as a witness..no need to get in the hoistway etc. If it trips within the correct range then there must be an external reason ( it is suspicious it only happens at night) . If it trips at lower than range speed them you are within your rights to ask them to rectify the fault ( new governor or recalibrate existing one ) . There is nothing wrong with asking questions of your service company especially as it sounds like you spent a lot of money with them .