This(=attach file) is guest screen.

Guest entered email and registered private topic. Guests can view registered topics in the topic list.
However, if a guest registers a private topic without entering an email, the guest cannot view the topic in the topic list. (Admin can view all topics list at any time)
Is it normal to see the list according to whether the guest writes an email or not?
If this is normal, how can a guest who did not enter an email write a reply?

Posted by: @tayo

I set it up so that guests can register private topics.

What is this? Guest cannot create and see private forums, that's just impossible. They'll not see replies of other admins and moderators in private topics. wpForo cannot be used in this way. You should not enable private topics for guests.

Guests don't have UserID in the database so the system cannot control and authorize not-logged visitors to show private content. That's why wpForo doesn't support guest private topics.

@robert

Oh, I'm sorry. I didn't have enough explanation for the situation in my question. I'll explain it again.
I have created a specific private forum for guests and an additional forum access for guests who can use this forum. So all access settings can be activated. Anyway, this forum access allows guests to create topics('Can create topic') and only check their private topic checkbox('Can set own topic private').
The reason why I did this is because I needed a forum where guests needed to write private topics.

Now, I want you to read my question again. I believe you can understand enough.

Question1. 

Posted by: @tayo

I set it up so that guests can register private topics.
Also, I checked "Can view replies". However, guests can see their parent reply, but not their child reply. In other words, replies of replies are invisible.
If admin change it from private to public, guest can see all the parent and child replies.
Could you check this for me?

I attached the screen of the guest and the screen of admin, respectively. This will enable you to quickly understand my problem.

Question2.

Posted by: @tayo

Guest entered email and registered private topic. Guests can view registered topics in the topic list.
However, if a guest registers a private topic without entering an email, the guest cannot view the topic in the topic list. (Admin can view all topics list at any time)
Is it normal to see the list according to whether the guest writes an email or not?
If this is normal, how can a guest who did not enter an email write a reply?

Let me know if you need further explanation of the problem. Thank you.