Hi,
Sorry, I don't want to waste your time, so I always check the most common issues first. From your screenshot, that looked like the most common issue.
I just tested in a new, empty project with Dialogue System 2.2.16 and spine-unity-3.8-2021-04-30.unitypackage, and the example scene works correctly.
I don't want to waste your time, but I don't know where to go from here, so I have to ask all the questions I can think of.
Are there any errors or warnings in the Console?
When you play the example scene, does NPC1's Canvas > NPC1SpineGraphic move in the Hierarchy to become a child of Subtitle Panel 2? (See image below.)

- spineSubtitlePanel.png (28.07 KiB) Viewed 1581 times
Can you send a
reproduction project to tony (at) pixelcrushers.com.
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https://discord.gg/FwUaCNt