After updating to 9.8.5, on Emacs 29.3, I now see this org-element--cache warning several times the day; usually when exporting as Latex file. Emacs still displays the warning if I kill the buffer with section Emacs warns about and try to export an unrelated org file.
If I start a fresh emacs, I again can export the file Emacs initially warned about. Unfortunately, I still do not know how to reproduce the warning reliably. But I wanted to wait with this report, because I noticed in the archive that people now and then encountered this error since quite some versions. I hope I can provide more info next time. Thanks for your time! -- Karl Eichwalder
