This happens randomly - I have never reproduced this but the users are in the system a lot more than me. 

A document is created with a load of fields on it, and there are 2 rich text fields. We're using Domino 8.5.3 - there are no extension lib controls in use. The document has workflow built in, and all validation is done by a SSJS function called from the data query save event.  There is an insane amount of logging to the sessionscope.log and also this is (now) captured for each user in a notes document so I can review what they are doing. 

Sometimes, a user gets to a workflow step where they have to fill in a Rich Text field and make a choice in a dropdown field, then they submit the document with a workflow button. When  the workflow button is pressed (does a Full Update) some client side JS runs first 

    // Process any autogenerated submit listeners

    if( XSP._processListeners ){ // Not sure if this is valid in all versions of XPages

    XSP._processListeners( XSP.querySubmitListeners, document.forms[0].id );

    }

(I added this to try and prevent the RTF fields losing their values after reading a blog but so far it's not working)

then the Server-side event runs and calls view.save() to trigger QS code (for validation) and PS code to run the workflow agent on the server. 

95% of the time, this works fine.

5% of the time however, the page refreshes all the changes made, both to the RFT field (CKEditor) and the dropdown field are reloaded as they were previously, with no content. It's like the save hasn't happened, and the Full Update button has decided to work like a page refresh instead of a submit. 

Under normal circumstances, the log shows that when a workflow button is pressed, the QuerySave code starts and returns True. Then the ID of the workflow button pressed is logged (so I can see which ones are being used when I am reviewing problems), then the PostSave code starts and finally returns true. 

When there is a problem, The QuerySave event runs, returns true if the validation has passed, or false if it's failed, and then it stops. The ID of the workflow button is also logged. But the code should continue by calling the PostSave function if the QuerySave returns true - it doesn't even log that it's starting the PostSave function.

And to make matters worse, after the failure to call the PostSave code, the next thing that is logged is the beforePageLoad event running and this apparently reloads the page, which hasn't got the recent edits on it, and so the users loses all the information they have typed! 

This has to be the most annoying problem I've ever encountered with XPages as I can find no reason why a successful QuerySave (or even a failure because mandatory fields weren't filled in) would cause the page to refresh like this and lose the content. Please please can someone help point me in the right direction??