Hey Gerold,
first of all, thank you for choosing Ikebana!
The issue looks like the bug where the infinite scroll had been interacting with projects that have the “sticky” attribute set to active; it was fixed in the latest versions of the theme – please try updating your instance of Ikebana to version 3.3 (you can download the latest version from the “Downloads” tab of your ThemeForest account), it should solve the issue. If you encounter any difficulties during the theme update process, please let me know! Alternatively, you can provide access to the ftp account connected with the website in question, and I will update for you.
Sincerely,
Andrii / Satori Studio