For quite some time I have the below warning on buildwidgetSet in Studio when assembling the project. I seemed to have no effect, so I did not pay attention but it might have an impact though.
Today I migrated from 6.8.5 to 6.8.7 and the widget set was not built any more, neither copied in war file (buildWar). So I had the infamous “resource not found […] AppWidgetSet […]”.
Clean then reassemble did nothing. buildWidgetSet was still claiming UP-TO-DATE. So I finally made a dummy change in AppWidgetSet.xml, and reassembled, it worked.
Not sure if the migration forgot to clean something, or if the below message is involved.