After preview node is not saving the content.
This is an error that comes from the node module.

The error occurs when you submit the node form and the node has been changed by something since you loaded the form.

The change could be caused by another user editing the content, you editing it in a different tab/browser, some background task editing it, etc.

How it happens is:


You load the node edit form. The node object is pulled from the database at this time.
You make the changes.
You save the node.
The system checks the last changed date of the node object that was loaded when you loaded the edit form (in step 1) with the last changed date for that node directly in the database (the current last changed date).


It does this to stop two people changing a node at the same time, in which case one persons changes might accidentally override the other persons.

To get around the error, you have to refresh the node edit form and make your changes and save it again.

There is no way around it but there are ways to lessen the annoyance of getting to the end of an edit and being told you have to refresh.
One such way is the content locking module.

That module makes it so that when you load a node edit page it "locks" that node, so if someone else goes to the edit page while you have it locked it will give them a warning and won't let them make edits until you have finished editing and the node is unlocked.

This means you won't waste time on an edit that you won't be able to save.