OneCalendar (iOS): Old data (contact birthday) remained when actual contact was removed.

OneCalendar (iOS): Old data (contact birthday) remained in OneCalendar when actual contact was removed. Calendar sync was with Google Calendar. On browser, Google Calendar did not show the birthday after the contact was remove, but the info still remained in OneCalendar (iPhone). The only way to remove was to remove the Google calendar account, then add back to resync all data.
I'm wondering if this could be a local iOS cache data issue?