Cisco nexus vPC peer-gateway causing flooding

I have posted question here because i not able to upload diagram image on reddit. : https://networkengineering.stackexchange.com/questions/58945/does-vpc-peer-gateway-causing-unicast-flooding

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This is very interesting stuff i am seeing so stay with me while i explain you, following is my network topology where i have SW-1 is configured for HSRP for multiple VLANs, SW-2 & SW-3 connected to SW-1 using vPC. Last few month i am dealing with this unicast flooding where whenever i add new switch in network or spanning-tree changed i noticed for 5 second or so all my switch ports seeing entire network traffic like traffic get mirror on every single switch in datacenter.

after collecting lots of data i found this flooding only happening in one side of network which is SW-3 so whatever TOR switch connected to SW-3 seeing unicast flooding, after comparing configuration i found only one parameter is missing in SW-3 which is peer-gateway.

I have no idea that is the issue but i want to see what you guys suggesting, i thought peer-gateway is only for HSRP switch not for L2 switch.

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SW-1

vpc domain 1

peer-switch

role priority 10

peer-keepalive destination 172.29.0.7 source 172.29.0.6

peer-gateway

auto-recovery

ip arp synchronize

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SW-2

vpc domain 2

peer-switch

role priority 10

peer-keepalive destination 172.29.0.103 source 172.29.0.102

peer-gateway

auto-recovery

ip arp synchronize

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SW-3

vpc domain 3

peer-switch

role priority 10

peer-keepalive destination 172.29.0.161 source 172.29.0.162

auto-recovery

ip arp synchronize

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Do you think peer-gateway missing option causing unicast flooding on SW-3 switches? ( I have multiple TOR switches under SW-3 and all those switch also seeing flood)