Servers configured inside MaaS does not came up after rebooting maas server

We had an incident a few days back wherein we had to reboot the MaaS server.
However, after the server came up we have observed that few of the deployed servers inside MaaS UI did not come up.
Why rebooting MaaS server will make the deployed servers unreachable?
Is there any way we can avoid making the servers unreachable when we reboot the MaaS server?