An update is now available for the ASUS ZenFone 2, and it makes the phone even more stable. The update is about 103MB in size, and can be downloaded over-the-air now. An official changelog for this version has yet to be posted, but @ArunKmRathi notes that this addresses system stability.
If you are rocking the ZenFone 2, be sure to check your phone now for an update. To check manually, head into the Settings, then About phone and finally check for the update.