In just the past week, I’ve seen at least two situations where customers suddenly had their Generate -> Image Assets and Generate -> Edge Reflow Project disappear (or become disabled).
The first thing to troubleshoot in this case is to look at your preferences. Go to the menu item Photoshop -> Preferences -> Plug-Ins
In the dialog menu, ensure that “Enable Generator” is checked. I’m sure there is a bug somewhere, but, this preference gets turned off sometimes!
Hopefully, this helps.
In the case of exporting Edge Reflow projects, if you are not able to see a menu option for File -> Generate -> Edge Reflow Project, please check that you have the folder: <install directory> / Adobe Photoshop CC/ Plug-ins/Generator/reflow.generate. If you do not have this directory, uninstall and reinstall Edge Reflow. The Edge Reflow installer should automatically install the plug-in for you.