SharePoint - SharePoint 2013 workflow error - Failed to load the workflow definition

Hi,

I am using SharePoint 2013 online version. I have created List Workflow using SharePoint Designer 2013.
While working on workflow, it was able to edit, publish multiple times. But next day it started giving error :
‘Failed to load the workflow definition for the workflow’. Now I am not able to edit workflow. What may be the issue. 
I again created new workflow as I was not able to edit the previous one. Again the issue repeated for new workflow too.(i.e. editable on same day, but started giving error on next day) Note: Current attached workflow instance is working properly only the thing it is not allowing to edit the workflow.

Error snap is attached herewith,

error:

‘Failed to load the workflow definition for the workflow’.  After clicking OK it gives message ‘SharePoint designer cannot display the item’.

One possible cause is that the workflow rules file of the workflow that you are trying to open contains invalid XML markup.

Possible Solution

In Office SharePoint Designer 2007, in the Folder List, click the plus sign (+) next to the Workflows library to expand it, and then click the plus sign (+) next to the folder of your workflow to expand it.

Double-click the rules file to open it.

The rules file name is typically Workflow_name.xoml.rules.

Right-click anywhere on the page, and then click Verify well-formed XML.

Correct any errors; then save and close the file.