I have about 40 QGIS2 projects. If I open them with QGIS3 labels and svg icons are not displayed. I don't know if there is any other feature that is not working when upgrading to QGIS3, but I suppose there must be more of them.
For labels, for example, I can see no configuration in QGIS3, as if labels config was not defined in the layer. Seems that QGIS3 does not understand that part of the layer configuration saved in QGIS2.
Is there any tool/procedure to upgrade a QGIS2 project to QGIS3?