City dropdown bug (null values) with multi-country database on Osclass 8.3

Hi everyone,
I'm developing a classifieds portal based on Osclass with the goal of covering all European countries. To do this, I populated the location database by importing the various countries using Osclass's native functions (States/Regions/Cities).

The problem:
When editing the user profile (or posting a listing), I'm experiencing unusual behavior in the dynamic drop-down menus. After selecting the Country and Region, the City menu doesn't load the correct names but displays a list of null values.

Practical example:

Select: Italy

Select: Lombardy

Result in the City menu:
null
null
null
...


The problem seems to occur intermittently or only with certain countries/regions. I've already tried different themes, both the default one and other free ones, but the same error always occurs, so I think it's not related to the theme.

I'm using version 8.3.1 with the zara theme.

Has anyone else encountered the same bug? Could it be a character encoding issue (UTF-8) or a database limitation given the large number of European records?

Thanks in advance for your support!

Would it be possible to transform the field where you enter the city into a simple text field and not have all the cities loaded when you choose the region?

There is possiblity, but you have not added url nor screenshot or function you are using, so it's quite hard to help you