I have been having a ~fun~ quirk since the latest Apple operating system update where PDFs' text disappears when you open the file (example graphic attached).
Yeah, I've seen this (Ventura 13.2). I have no 'permanent' solution but closing the file (not the preview app) and reopening it seems to fix it. Alternatively and until Apple pushes a fix you can use a browser to open PDFs.
No matter OS version or platform, seen a number of threads where Apple has a hard time rendering certain PDFs. For example, this thread from 2018 and a PDF made with "for professional printing" (PDF used to make brochures) was not viewable using stock iOS functionality.