Bullets Pager in WordPress 5 not working anymore

I have to service an older site, which is currently running WP 3.26.

While testing the update to 5.03 I recognized that the graphical pager i.e. Bullets isn’t working anymore only the thumbnails.

Compare:
Original-Site: https://blumeundspaten.de/text/
Staging: https://bus.roemling.org/text/

Can anybody confirm? Does anybody have a workaround for this?

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