Each time I was able to complete the following steps: I tried deleting my Google account from the mail (or calendar) app, by going to 'settings -> accounts', and then re-creating the account. For a while I was able to sync my Google account emails (Gmail) and calendar in those apps, but about a week ago, it has stopped working: the calendar is empty (no events, and no calendars listed), and the emails that were already synced are still there, but syncing doesn't bring any new email.
I'm having a problem with the default Mail and Calendar apps in Windows 10.