You may see ESXi disconnect then connect automatically in vCenter within fraction of seconds.

Following lines can be seen in VPXD.LOG

info vpxd[7F20FA9D3700] [Originator@6876 sub=HostCnx opID=CheckforMissingHeartbeats-713e154b] [VpxdHostCnx] No heartbeats received from host; cnx: 5254c90c-d813-51e1-1e6b-0cc0a8e9b10f, h: host-984, time since last heartbeat: 14356285014ms
info vpxd[7F20FA9D3700] [Originator@6876 sub=HostCnx opID=CheckforMissingHeartbeats-713e154b] [VpxdHostCnx] Marking the connection alive to false: 5254c90c-d813-51e1-1e6b-0cc0a8e9b10f
info vpxd[7F20FA9D3700] [Originator@6876 sub=InvtHostCnx opID=CheckforMissingHeartbeats-713e154b] [VpxdInvtHost] Got lost connection callback for host-984
warning vpxd[7F2118B73700] [Originator@6876 sub=InvtHostCnx opID=HostSync-host-984-f11f4fd] Connection not alive due to missing heartbeats; [vim.HostSystem:host-984,esxi.mydomain.local], cnx: 5254c90c-d813-51e1-1e6b-0cc0a8e9b10f
warning vpxd[7F2118B73700] [Originator@6876 sub=MoHost opID=HostSync-host-984-f11f4fd] [HostMo] host connection state changed to [NO_RESPONSE] for host-984
info vpxd[7F20FB468700] [Originator@6876 sub=vpxLro opID=lro-30458735-12d91ab0] [VpxLRO] -- FINISH lro-30458735
info vpxd[7F2118B73700] [Originator@6876 sub=InvtHostCnx opID=HostSync-host-984-f11f4fd] Succeeded restoring heartbeat; [vim.HostSystem:host-984,esxi.mydomain.local]
info vpxd[7F2118B73700] [Originator@6876 sub=MoHost opID=HostSync-host-984-f11f4fd] [HostMo] host connection state changed to [CONNECTED] for host-984

This happens because of network issue between ESXi host & vCenter server. Temporary workaround is to set heartbeat timeout as per KB

vSphere Client:

Open the vSphere Client. Connect to vCenter Server.
Select Configure then Advanced setting under setting.  If following key isn’t present then create it manually.
Click Edit.
Name config.vpxd.heartbeat.notRespondingTimeout
Value 120
Click Add then OK. Restart the vCenter Server service.

#esxi-disconnect, #vcenter