Although there appears to be no clear answer there has been some suggestion that this is down to a cached version of the universe on the server. The cache is cleared/refreshed at set intervals and if you export at the start of another cycle then it will take a while for the changes to be seen.

This is what would appear to cause the inconsistent time delay between making and exporting changes and them being seen in the dashboard designer.

Other suggestions could be to log off and back on again.