Proxysg doesn't offer DHE ciphers while contacting the upstream server.
In the pcap , you can see DHE ciphers are being offered by the older browser clients but Proxysg doesn't offer the same DHE ciphers to the upstream server.
It was working on 6.x but not 7.x
7.x Proxysg OS release
DHE ciphers are disabled on 7.x by default.
Execute this command below to enable DHE ciphers
proxy dhe-ciphers enable