Is there any issue to put / as a home directory of root user from security point of view instead of /root
Yes. /root has 700 permission (rwx------) whereas / has 555 (r-xr-xr-x) permissions for all users.
Now if you use various common utilities you would have /root/.config with rwxr-xr-x permissions. If you were in /, that directory becomes accessible to anyone on the server, whereas if it was in /root it would not be.
Having root's data accessible to any user is a security risk.
Note that /root/.config is an example, there are many other folders, folders as diverse as any one of hundreds of thousands of possible programs that root can run.
Yes, technically it is security by obscurity. But for example, would you send me the IP address of your server please? Why not? Why do people obscure IP addresses and server names etc in posts?
For the exact same reason you don't want unauthorised people accessing root's data. The same reason you don't hand out a network map. If roots data is not secure, you must vet every single program to ensure it secures it's data properly instead of just knowing it's safe because it's in /root.
In the case of root, root is the gatekeeper, guarding all the doors, holding all the keys. That's why root is a big fat target for everyone trying to hack a server.
In warfare you never give your enemy anything. He is not to know when your patrols are scheduled, when your convoys are due to arrive, where your potatoes come from, what time breakfast is served, what time the guards are changed, where your main powerline runs, which tent or barracks belongs to the commander, who the commanders driver is, what jeep does he drive, anything.
In counter intelligence we want the enemy to know nothing about us at all, because through the long history of the world we can find many many examples of how what has been thought to be the most trivial piece of information has been used to bring down kingdoms, destroy nations, assassinate kings and win battles.
So ask yourself this question. Which is more secure?
The choice of whether or not to restrict access to any information about root, roots activity or roots data should be trivially obvious. No professional answer can be otherwise.
It is my understanding there are severe problems if you ever log in to X as root with root's home directory set to /. In the old days the protection provided by /root was considered unnecessary and having root's home dir as / was merely untidy but not so much anymore. root didn't used to have full sessions but now he does if some people misuse the system.