IPv6 neighbor status failed

I am terminating a vxlan on a mikrotik ros7. the vni is bridged with the an port. That port is connected to a hap ac2. on the hap ac2 port connected with the rosv7 routerboard, I add ipv4 (/24 mask) and ipv6 (/48 subnet) address. However, there is a strange problem! I can ping remote hosts within the same subnet over ipv4. I cannot ping remote hosts over ipv6 and I get the folowing failed status! If that host pings my ipv6 address first then its mac address is added to the neighbor table and I can easily ping it as long as the entry doesn’t expire. Please help me! Check the attachment.
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