openwrt wget returned 4
https://forum.openwrt.org/t/opkg-update-fail-wget-returned-4/114447
The "standard wget" in OpenWrt does not come from busybox, but is a small OpenWrt specific small tool uclient-fetch. It seems to fail under some IPv6 configurations. Great that the full GNU wget-ssl worked for you.
opkg install wget-ssl
opkg install libcurl4
Failed to download, wget returned 4
https://openwrt.org/faq/failed_to_download_wget_returned_4