Found the problem. it was the plugin nodebb-plugin-merge-subtopics
It could load any category page with sub-categories in it.
Maybe it's hepfull for somebody who has same problem 🙂
Hello all, I am Dilip. Hope I will be able to learn from your guys.
And my thanks for Phsycobunny for his excellent effort.
Hi dilip
@meetdilip thanks but its not just me
Meet the team:
https://github.com/designcreateplay/NodeBB/graphs/contributors