Yes I still have same issue. But I have learned to live with it, so to say.
First trace is correct, then fortigate stops to respond and after while (could be 30 minutes - some day) it respond again.
This is easy to see since I run pingplotter monitoring thru fortigate unit and it records route change whenever fortigate responds to icmp or not. It's hop will be replaced by next router, as you saw also.
I think it still relates that fortigate offloads traffic to asic and that's why it doesn't respond. But I'm not sure why it starts to respond after awhile again.
There is no asic offload disable possibility under firewall policy in our unit (100D) for some reason.
We have also 600D unit and in that there is possibility to disable offloading.
I might open support case to fortinet at some point but this hasn't been major issue for me so I haven't done that yet.
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