I found the search function doesn't work a couple weeks ago. The store has been online for just over a year. I didn't spend much time maintaining the website in that year.

I did a one click install on the previous host, I added all the data manually. The day before, my site was shut down because the domain was transfered. I followed https://www.zen-cart.com/content.php?142-i-want-to-move-my-zen-cart-installation-to-another-host-or-a-different-server instructions to transfer whole store and data to the new host company. This time i installed zencart manually, I restored my database and my site. I checked my logs and there are no error files.

I wonder if Multiple Categories Link Manager add-on is the cause of the problem.