MINE does it too.. not very often but i have to reboot it on start up and it helps
also since updating to as i call it elCRAPitan
i have been unable to play sims 4 at all, upon opening it it just crashes and gives me the report form
prior to having my imac download elCRAPitan it ran absolutely fine, no crashes on anything. i even spoke to apple and the simswhich confirmed it is an elcrapitan problem and they both told me to just wait out the issues and wait for "patches" ...here i am 3 months later, many updates, still happening!! ugh.😡