Can't find package lists after upgrading to 19.07

[tmomas]

@weka

wget returned 4.

Opkg update error (wget returned 4)

I just upgraded from OpenWRT to LEDE and faced the same error. The download fails randomly but not always. Finally I found that it's caused by malfunction IPv6. Tried nslookup the download hostname, it returned both IPv4 and IPv6 addresses. But my ISP doesn't support IPv6 so it couldn't download. I added option ipv6 0 to disable IPv6 for the network interface in /etc/config/network. Opkg works after restart.