Try upgrading to Mx 7.7.1 to see a more detailed error message.
From the release notes:
"We improved the error message that is logged when the change hash for a certain change is not sent from the client to the server. It now includes the entity and member name to which the change belongs, which makes it easier to find out which change caused the error. (Ticket 55679)"
I think that happens when an object attribute, which is readonly, is changed client side. But there have also been some issues with this prior to 7.5.
See also the release notes for 7.7.1 - you could try with that version.
Hi Ritchie, I had simular with one of my applications. The issue seemed to be that a read-only attribute was used in a widget which tried to edit the value. I set the attributes used in the widget (Dropzone) to read / write, that solved the issue.
ps. still using 7.5.1, so upgrading not needed.