Hi W.M.K,
I'm currently at work, but I will look into it further once home.
The error itself suggest, that some Techtree UIDs don't match with the UIDs the actor has assigened to him. Those need to match. Check this and adjust.
The techtree in the demo uses the UIDs HOLY and HEALER. The notetag would be like this then:
<techtree>
HOLY
HEALER
</techtree>
If this still doesn't work, can you replicate the error in a fresh project with just the techtree plugin?
Can you send me a download link to your project or the Techtree.json?
Are there any other console warnings or messages?
Best regards,
Felski