When writing a post, you need to refresh it to be able to write a post.
If you do not refresh, the Add Topic button does not respond.
Exclude wpForo from your cache plugin.
Check this FAQ About Cache: https://wpforo.com/community/faq/wpforo-and-cache-plugins/#post-37150
Post a url so we can check.
Could the captcha invalid key owner be the issue?
Also, since i can't register and test it due to your KR language, you could press F12 and watch your browser console for ERRORS before pressing Refresh. And let us know.