No internet for lease while migrating to ubiquiti airgrid

Hello All,

I am experiencing an extremely strange problem with one of my network premises. I have a wired fiber backbone network across several buildings. there are several unify AP wifis connected and controlled by unify controller.
Unlike other buildings., there is one building that has wireless connectivity using ubiquiti AirGrid instead of Optical Fiber.

That building has only one AP. The problem is when a client has got lease from mikrotik through that AP, it gets internet in that building but not in other buildings until his lease has to be deleted and client obtains a new lease. It happens accross all devices like phones, wifi laptops, macbooks, basically everything. Same applies viceversa. If a lease obtained device from mikrotik through any of other buildings APs connected through optical fiber comes to that building, it behaves the same. After deleting his lease, he gets internet.

Can any one help me understand the problem?

My device is Mikrotik RB1200. ROS version 6.24