Pagination freezes

I have a very strange error…

Last night I was updating old articles, and splitting very long text into pages using <!--nextpage-->.

It worked absolutely fine, except of one article.

Here the link to a page it works: https://www.fussballwitwe.com/wetten-mathe/laender-sitten/

3rd page of this article is frozen: https://www.fussballwitwe.com/wetten-mathe/laender-sitten/3/

Every other page works .All other articles through the website work, both languages. Third page in this article is the only one which doesn’t.

I tried to copy the text into a new article. It still freezes.

I removed the pagebreak, and then page 2 sometimes freezes, and sometimes not.

Any ideas what this error may be? I’m totally lost…