Seems like hardware issue.
1- Use a different switch port and a new network cable to isolate cabling/port issues.
2- When ZD is in the problematic state, try connecting console cable and access the ZD and then try to ping gateway, run below commands which will provide more information.
netstat Displays the network status.
show sysinfo Displays current system status.
show ethinfo Displays current system ethernet status.
show techsupport Displays current system options and status.
monitor sysinfo Monitors current system status.
Check on switch side if there is any broadcast storm which is causing port hang or ZD hang (due to high CPU/mem utilisation).
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