openwrt.orgかな？ISRG Root X1で署名されてるっぽい。
$ :| openssl s_client -connect openwrt.org:443 -servername openwrt.org > /dev/null
depth=2 C = US, O = Internet Security Research Group, CN = ISRG Root X1
verify return:1
depth=1 C = US, O = Let's Encrypt, CN = R3
verify return:1
depth=0 CN = lede-project.org
verify return:1
DONE