Odoo 10, Event Calendar and List Snippet and Iframe only shows List without Calendar

[Highcooley]

The Event Calendar Snippet only shows the event list without the calendar to the left:

The issue was resolved after a single entry (not related to events) was made into the calendar module

[Highcooley]

No, sorry...keeps vanishing again

[abhijith708]

I have the same issue the calendar is not visible, I'm getting following error !!!!!
odoo version 10
web.assets_frontend.js:519 Uncaught TypeError: Cannot read property 'dateFormat' of undefined
at dataToOptions (web.assets_frontend.js:519)
at init (web.assets_frontend.js:502)
at new DateTimePicker (web.assets_frontend.js:638)
at HTMLDivElement. (web.assets_frontend.js:638)
at Function.each (web.assets_common.js:370)
at jQuery.fn.init.each (web.assets_common.js:358)
at jQuery.fn.init.$.fn.datetimepicker (web.assets_frontend.js:638)
at Class.render_calendar (web.assets_frontend.js:51)
at Object.proxy (web.assets_common.js:380)
at fire (web.assets_common.js:541)

[github-actions]

There hasn't been any activity on this issue in the past 6 months, so it has been marked as stale and it will be closed automatically if no further activity occurs in the next 30 days.
If you want this issue to never become stale, please ask a PSC member to apply the "no stale" label.