Solved!
After 2 hours of attempts figured out that the “-” sign in the first heading was the cause, as soon as I removed it and replaced it with “:” the TOC started to appear.
Also another problem I solved along the way is the color of the Title of the easy TOC “Table of Contents” – it was white on white for me.
To change the colors to your liking just choose the “Custom” theme option in the settings of the plugin and then you can use the coloring options in the Settings to tweak the colors. Hope this helps! 🙂
I have also noticed that when I view the post through the templates I can see the menu, but not in the live post or in the post editing screen…
Screenshot: https://imgur.com/a/6LNgmko
P.S. The question is still relevant
Worked for me aswell, by removing the ' just in the first headline! (No need to remove it in all of the headings) I would be glad if this could be fixed in the next plugin update 🙂 Thanks a lot for the support.