network connectivity problem in the network

Question

for two months I have a problem with connectivity in my network. my PCs take the Ip address configuration, but randomly they cannot ping their default gateway, nor the PCs in other vlans nor connect to the internet. I have several vlans in my network and routing is done by the 3 stacked core flex fabric 5700 switches. all the network is HPE with are connected to a Fortinet failover firewalls.
The problem gets solved by itself after around 1 hour without any sign how it starts to work again.
At the beginning I suspected the DHCP on AD controllers, but I have the problem even with fixed ip addresses.
I saw same question asked in here but no definitive solution:
https://social.technet.microsoft.com/Forums/windows/en-US/609e1fcf-bb04-4b25-8a1b-97ae5687a8ed/some-computers-on-network-cant-ping-gateway?forum=w7itpronetworking

Answer 1

cannot ping their default gateway I suspected the DHCP on AD controllers

If you cannot ping the gateway then this seems a hardware problem. Could be bad cables or a problematic switch.

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