had some issue, maybe someone had faced this issue before :
my one of switch was unreachable for 3 days , but ap is working fine, any sugestion?
switch model :ms220
Unreachable just means it cannot communicate to the cloud for some reason. Make sure you have no ACL or firewall rules blocking the management IP address of the switch. Try pinging it from upstream. The fact that your AP downstream can connect to the cloud means it still forwarding traffic, just not able to communicate with the cloud.
You can open a support ticket to have the team look at it and see why its an issue.
Have you check the status of your DHCP server and make sure that your management IP addresses in your DHCP pools are not exhausted. Also, what is the LED status of your switch?
I had this behaviour sometimes before firmware version 9.32 with MS220 switches. I needed to do an cold reboot.