ProxySG's failover environment is using VIP address.
When master unit takes back mastership from standby ProxySG, Network traffic may get slowness or breaks.
Under multiple ProxySG units redundancy deployment using SG redundancy Protocol(SGRP) feature, our admin-guide document shows.
If the group master fails, the slave with the highest priority takes over (after approximately three times the interval value).
The failover time of the group is controlled by setting this value.
So, if advertisement interval sets 40 seconds as default, when master unit goes fails, slave / stand-by unit takes mastership of traffic after 80~120 seconds later around.
On the other hand, when master unit backs to network as alive, it may be also take back mastership of traffic with some delay because of multicast and VIP Gratuitous ARP advertisement packets sent out timing to network. After those first information was out from master unit, the unit does work as highest priority machine for proxy traffic.