Web Parts added to page disappear randomly, and Object Does Not Exist error.

Hello,

We have been troubleshooting issues when adding web parts (widgets) to a page, the changes are not always sticking. Intermittently, the webparts will just disappear and there appears to be no version history to restore them from. A secondary issue using the same repro steps, is an error "The object does not exist. It may have been deleted by someone else". Both of these issues happen intermittently.

We've tried everything under the sun to fix this. So, I'm really hoping somewhere out there is someone who's seen similar behavior and has some new suggestions.

Steps to reproduce:

1. Open a Page to edit
2. Add a new Widget. Fill out all required details.
3. Hit Save and Continue (with Refresh checked)
4. Note the widget is usually (but not always) there after first save.
5. Save the page. (can also repro when skipping this step)
6. Add or edit another widget on same page. Note that often, both the new and previous widget disappear. Or, sometimes, an "object does not exist" error.

More info:

• Repros in multiple environments (web farm and non-web-farm)
• We've made considerable efforts to reduce database size and other performance improvements. Page Performance is much improved but the issue remains.
• We've debugged the code in a debugger. Nothing obvious going on.
• We've looked through console logs, etc
• We've examined the Event Log again and again, with no errors logged seeming to be connected.
• We've disabled all non-essential front-end scripts when in Edit mode
• We've reviewed every kind of configuration we can think of.
• Kentico 10, .Net Web Forms, Single SQL DB, 1-2 web farm servers, ASP.Net session state, no EMS, was originally built on Kentico 7 and upgraded. Issues started appearing randomly and cannot be definitely tied to any code release.

Let me know if anyone has any suggestions on a potential cause or fix. Thanks!