When you collapse a chapter and open it back up, the spacing of the elements is off. I used chapter 236 here to demonstrate. This is repeatable across Safari, Chrome, and Firefox versions of the mobile site
Pretty sure, at this time, all browsers on iOS/iPadOS are still just safari (let me know if I am wrong please). Anyway, that aside I am not able to reproduce on Android using Firefox, Chrome, or Edge. So looks like an iOS Safari issue.