In /logs/firmware/unblob_extracted/firmware_extract/1568982-13971496.squashfs_v4_le_extract/etc/uci-defaults/20_migrate-feeds line 5:

echo -e "# Old feeds from previous image\n# Uncomment to reenable\n" >> /etc/opkg/customfeeds.conf

     ^-- SC3037 (warning): In POSIX sh, echo flags are undefined.

For more information:

  https://www.shellcheck.net/wiki/SC3037 -- In POSIX sh, echo flags are undef...