Using V11 Community, I have just started receiving this error when I test to click the preview on the templates of Email :

Failed to render template using values {'format_date': . at 0x7f5ee472dd08>, 'format_tz': . at 0x7f5ee472d840>, 'format_amount': . at 0x7f5ee472d158>, 'user': res.users(1,), 'ctx': {'lang': 'en_US', 'tz': False, 'uid': 1, 'params': {'action': 95}, 'template_id': 38, 'active_model': 'mail.template', 'active_id': 38, 'active_ids': [38], 'search_disable_custom_filters': True, 'safe': False}, 'object': res.config.settings(45,)}

I have not change anything on the template. Have  no idea what could have changed to start causing this nor where to look to correct it, any ideas/direction would be appreciated.