Just a datapoint, with 50 instances, 50 FIPs, 50 routers on a single node, restarting OVS agent causes it to drop traffic for 10-15 seconds while the physical bridge flows are rebuilt. If you want to see this more clearly, put a 10 second sleep into root wrap and restart the OVS agent. In that scenario you can see the problem even with one instance.
Just a datapoint, with 50 instances, 50 FIPs, 50 routers on a single node, restarting OVS agent causes it to drop traffic for 10-15 seconds while the physical bridge flows are rebuilt. If you want to see this more clearly, put a 10 second sleep into root wrap and restart the OVS agent. In that scenario you can see the problem even with one instance.