I don't believe it's the WAN links because you can see the packet loss inside of the building when trying to ping any of the SVI's that reside on the core MS425 stack. It isn't simply packet loss to destinations outside of the building across the WAN links. I have tried what you suggested with iPerf to generate significant load on each of the WAN links. When I do this after hours, there are no issues. I'm very confident this issue is only present during regular hours, I suspect as the result of someone or something coming onto the network during the day The support engineers I've spoken with have all confirmed there is very high CPU usage on the master stack switch throughout the day. They've also confirmed it returns to normal load (~20%) after hours. One interesting change from moving to 10.16 firmware is that both switches in the stack are now showing significant CPU usage. This is very unexpected given that the slave switch shouldn't be doing any CPU intensive tasks while being a slave.
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