Am experiencing a problem with topics moved to a different category, once they are moved it is not possible for most users to reply to topic for some reason.
The category topic is moved to is set to permissions of only being viewable to trust tier #1 and above, not sure if that could be the reason or is some other setting/permission.
One user reported there was a reply option, but this displayed dialogue to start new topic with continuing discussion instead of reply.
Can you post a pic of your category security page?
Here it is, now see reply and create options are not enabled that must be the problem.
Figured this was probably a simple setting like that, little surprising that when new group is added permission default is they can only see not reply or create.
Edit: This does not seem to be the case when testing other category and adding new groups, default is when new group joins they can both reply and create. May be some other setting or reason why that would happen?
Have found that when everyone group is removed, that changes this default for settings when new groups configured for category.
Interesting haven’t seen that before. Typically when adding groups as you said. Norm in my XP is that the setting is see/reply/create enabled by default.
Never need to add admin group as they are typically not limited by category security setting. There is a theme-component that warns posting in closed topic & see only category. I have a few times as admin prior to adding it post where no one could reply. 
Seems to be they are indeed limited by these security settings, except for the admin account who moves topic to a category with these settings can still reply but other administrators cannot.
Edit: correction that is only moderators who can be prevented from being able to reply/create, not administrators.
No Admin accounts can post anywhere. Mods are limited by category security.
Just did a direct test. Admins group are not restricted accounts.
Remove Admins, Moderators and Staff.
Remove all TL except TL1 and enable reply & create. All users TL1 and up should be able to post.
Admins & Mods have full category access
If you create a Group say Group A and set category for custom Group A only to See/Create/Reply. An admin can still participate in this private category. Now if you want Moderators to be able to see/create/reply then you need to add that group to that private group’s category.
