This post was from November. Have you updated to a later version of Tableau Desktop and tried to republish? There is a known issue that was posted here - Known Issues | Tableau Software that looks like it could be the culprit. # 836626
I have the latest version of Tableau Desktop (2018.3.2), but I am still running into this problem even now. FYI, I am not using automatic size for my dashboard. All the sheets in my dashboard have a specified fixed size, although the specified sizes are different for the different sheets. Therefore it doesn't conform to the issue you mentioned above.