I believe I've solved my particular issue with Photoshop not opening a Vector Smart Object in Illustrator when it is double clicked. This is specific for Macs running Mojave OS (although it may help others). • Noticed when I right-clicked on an .ai file in my finder window and rolled over "Open With" it had Preview.app set as the default. For some reason, when I recently updated Sierra to Mojave it lost that setting. • Command-I opened file info. • Clicked on lock on lower right of info window to enable changes. • In section "Open with:" select Adobe Illustrator (select version). • Then hit button "Change All..." to make that the default. Reopen Photoshop and the file, double-click on your Vector Smart Object, and it should now open in Illustrator.
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