In /logs/firmware/unblob_extracted/firmware_extract/1568982-13971496.squashfs_v4_le_extract/usr/lib/opkg/info/nginx.prerm line 2:

[ -x ${IPKG_INSTROOT}/lib/functions.sh ] || exit 0

     ^--------------^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean: 

[ -x "${IPKG_INSTROOT}"/lib/functions.sh ] || exit 0

In /logs/firmware/unblob_extracted/firmware_extract/1568982-13971496.squashfs_v4_le_extract/usr/lib/opkg/info/nginx.prerm line 3:

. ${IPKG_INSTROOT}/lib/functions.sh

  ^-- SC1091 (info): Not following: ./lib/functions.sh was not specified as input (see shellcheck -x).

  ^--------------^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean: 

. "${IPKG_INSTROOT}"/lib/functions.sh

In /logs/firmware/unblob_extracted/firmware_extract/1568982-13971496.squashfs_v4_le_extract/usr/lib/opkg/info/nginx.prerm line 4:

default_prerm $0 $&commat

              ^-- SC2086 (info): Double quote to prevent globbing and word splitting.

                 ^-- SC2068 (error): Double quote array expansions to avoid re-splitting elements.

Did you mean: 

default_prerm "$0" $@

For more information:

  https://www.shellcheck.net/wiki/SC2068 -- Double quote array expansions to ...

  https://www.shellcheck.net/wiki/SC1091 -- Not following: ./lib/functions.sh...

  https://www.shellcheck.net/wiki/SC2086 -- Double quote to prevent globbing ...