Make sure that you have enough disk space as sync errors often occur when there is not enough disk space. It means you cannot predict how and when a crash occurs in Office 365 all these nasty flaws can appear at any time in any application. Office 365 applications keep crashing due to various glitches like Server downtime issue, viruses, corrupted files, third-party add-ons and lots more. You may have to restart your computer after the repair process is complete.