When we select cascading dropdown menus with 5 category levels on the listing page then there is a problem.
After selecting the 5th category, if we then come back to change the 4th category, as many times as we click on the 4th category, as many additional checkboxes appear.

Is this theme specific or same on all themes?

Yes, he does it in other matters as well

The problem also occurs in the Osclass Back office (Omega theme). When we have 5 category levels then it is not possible to edit a category by admin. It messes up the drop down menu.

Thanks, will look into that

Do we have any news about this problem?

Yes.
Tested and could not reproduce.
Make sure you use jQuery 3.x

Tested with jQuery 3.x.x and 1.x.x but nothing changed. The problem persists (Only in categories that have 5 levels)

As I explained, the problem also exists in the Omega theme in the Osclass management, (with jQuery Version 3.x .x and 1.x .x.) as a result of which it is impossible to correct the catecory of an object.

I tested with 4 levels and could not reproduce.

What do you mean by "could not reproduce"? Take a test with 5 class levels. Post an ad in the 5th category, then come back to fix the 3rd or 4th category of the same post and you'll see the problem.

Could not reproduce means, that based on your steps, it was not possible to reproduce such issue.

Have you tried with 5 class levels as I describe? If you have tried it with 5 class levels and it doesn't give you a problem then I need to look into whether there is a problem with my own installation.

I did a clean install of Osclass 8.2.1 with Sigma Osclass Theme 1.6.0 as the only theme. I saw the problem reproduced in the OMEGA theme's dropdown menu.

Enter the http://test0.gr/ site and start a registration by selecting the fifth category level. Before continuing go back to the second level of the same category and select another subcategory. See how it works. there's a problem