Expand (+) button appears on some pages but not others

Sometimes the spoilers expand just fine, and other times they don’t. I can’t figure out why.

For example, on this page, they work (both in the post text, and in the sidebar):

https://leifandthorn.com/comic/kudzu-roots-1-35/

However, click to the next page, and the sidebar spoilers won’t expand:

https://leifandthorn.com/comic/kudzu-roots-2-35/

On the main page, the sidebar works:

https://leifandthorn.com/

And then on the archive page, it’s broken:

https://leifandthorn.com/archive/

Any idea what’s going on?

The page I need help with: [log in to see the link]