Azure Grid member lose connectivity every day with Grid Master throught tunnel interface. It seems that problem is not related with network configuration as sync is working all day except specific periods of time during days.
This may caused by issue with the MTU value on VPN. Azure VPN default MTU is 1500, which is also default value for Grid VPN. Due to overhead, etc. on the VPN, you will need to set the Grid member to a lower MTU. Here is an excerpt from an Infoblox support article on this topic:
Cause
The Grid Member's VPN MTU size is inconsistent with what is being used by the Grid Master or network elements between the member and master.
Resolution
From member properties, reduce the member's VPN MTU size.
Because the VPN tunnel used for grid communications is UDP based, the MTU needs to be smaller than the MTU of the "link" it is riding across. If the link already contains other tunnels, the tunneling will consume "overhead", shrinking the available MTU for grid communications.
Adjusting the MTU for a member should be done to make sure enough bandwidth is available for grid traffic. The default MTU for Ethernet is 1500, but can be adjusted down to 1450, which should be able to account for one tunnel, plus grid communications. If the MTU on the underlying network is smaller, adjust accordingly.
