[Bug]: File list partially missing after opening a file in viewer until scroll

Bug description

File list partially missing after opening a file in viewer until scroll. Some folders that were previously visible become invisible. The file list appears truncated or partially blank.

Steps to reproduce

1. Have viewer and files_pdfviewer
2. Go to the Files app
3. Create a new folder named "Documents" and open it
4. Upload one or more files (PDF or text) that can be opened in the viewer
5. Create several subfolders such as "Dossier A", "Dossier B", "Dossier C", ... , "Dossier P" (the documents, to be opened, must not be visible when opening the folder).
6. Click on the folder name in the breadcrumbs (make sure you see the folder’s ID in the URL)
7. Scroll down to the uploaded file
8. Click the file to open it in the viewer

https://github.com/user-attachments/assets/d7fa3259-8ccb-4fc4-8034-c73c4dd1c22e

Expected behavior

No blank list.

Nextcloud Server version

32 / 31 / 30

Additional info

• Scrolling (with the mouse or keyboard) makes the missing folders reappear.
• After opening the file once, the file ID in the URL is replaced. If the page is reloaded at this point, the list loads correctly and no truncation occurs.
• Debug output shows that in the broken case the startIndex is 17, while in the working case it is 4.

Start by reproducing the issue in the Files app with files_pdfviewer, following the listed folder, breadcrumb, and viewer steps. Compare the broken and reloaded cases, including the startIndex values and file ID in the URL; done means the file list remains complete without requiring scrolling.