Batch conversion (--convert-to PDF) fails for read-only files (Impress)

The batch conversion works for writable files (.odp), but fails for read-only files (.odp).
In the following operation, the second conversion does not produce a pdf file.
A write permission is probably not necessary for a conversion.

$ ls -l aa*
-rw-rw-r-- 1 bob bob 11545 Sep 10 10:32 aa.odp
$ libreoffice  --convert-to pdf aa.odp
convert /home/bob/aa.odp -> /home/bob/aa.pdf using filter : impress_pdf_Export
$ chmod ug-w aa.odp
$ libreoffice  --convert-to pdf aa.odp
Error: source file could not be loaded

My environment:
Ubuntu 20.04.03
LibreOffice 7.2.0.4 fa0a9af5681a0acc7909a705f92c1ada8a658552

If I add “-n” or “–view” option before “aa.odp”, the “Document is read-only” popup appears. A click on “Open Read-Only” closes the popup, but the libreoffice seems stale for a long time, and I hit Control-C. No pdf file is created.

Any suggestion, other than changing the attribute?

I am wondering if this is related to the read-only popup notification added with 7.2.