@nemiere: Huh, that's weird.
Try to redirect the KFXMeta output to a file, by tweaking linkss/bin/cover-extract (with a proper code editor that won't mess up line-endings), by switching L#115 from
Code:
${PYTHON} ${LINKSS_BINDIR}/kfxmeta.py "${last_read_kfx}" "${LINKSS_TMPFS_CACHE}/"
to
Code:
${PYTHON} ${LINKSS_BINDIR}/kfxmeta.py "${last_read_kfx}" "${LINKSS_TMPFS_CACHE}/" &> /mnt/us/linkss/kfxmeta.log
And check what linkss/kfxmeta.log has to say about that after trying to reopen this book...