Commands 'set system ipv6 disable-forwarding' and 'set system option performance throughput' are mutually exclusive
At first
set system ipv6 disable-forwarding
Result from sysctl
net.ipv6.conf.all.forwarding = 0
Next
set system option performance throughput
Result from sysctl
net.ipv6.conf.all.forwarding = 1
From my investigation command 'set system option performance throughput' runs 'tuned-adm profile network-throughput'. It enables ipv6 forwarding.