Categories and Tags appear to have no posts assigned

I have migrated a blog from Blogger to Wordpress. Everything looks great, except categories and tags are not working properly. If I go to Dashboard > Posts I can see that all of the posts have assigned categories and tags. Archive pages for tags and categories work as well. However, if I go to Dashboard > Posts > Categories or Dashboard > Posts > Tags, all the categories and pages appear as if they have 0 posts assigned to them. The problem is with the front page as well - My front page is set to last posts, and everything works ok, except the categories above the post title do not show. It only say ‘‘Ni kategorije’’ = No category. Also, if I try using the tag cloud widget, no tags appear. What could be the problem? Thank you for you help!
The website is:

Hello there,

I hope you are doing well today.

This is a strange issue but it seems that categories were not transferred correctly when the website was migrated. Please try recreating the categories via Posts > Categories and the existing categories should be assigned to them.

Best Regards,