Is there any device connect between modem or client?
you direct connect ZyWALL310 between modem and PC to check SpeedTest again?
And make sure interface connection has auto-negotiated as1000M/Full. And also test it by different PCs.
Regarding to this case,
that it could be some
kind of connectivity issue between Zwall310 and Patch Panel.
Since from our test result, the upload
throughput can be go up more than 500 Mbps.
Therefore, we need your help to check what if you
use the PC to connect with Zywall 310 directly.