Form with long choice list seems to overload KoBoToolbox

I have created a form with 4 levels of cascading list from an XLS form. The selection tab has almost 6,000 rows. I have no problem creating the form in kf.kobotoolbox.org, deploying the form and adding data to it from KoBoCollect on my phone, and the cascading lists work fine. The problem is when I try to edit the form. It’s loading all the time and Firefox tells me that the page is slowing down the computer:

It is currently using only 11GB of the 16GB RAM on my i7 running Ubuntu 24.04.

After a few minutes it displays this contradictory information:

Is the issue on the KoBoToolbox server side ? Does it struggle with complex cascading lists? Here is the form, in case you want to test it.
Form_with_cascadinglists.xlsx (185,2 Ko)

EDIT: It is fully loaded after 5-10 minutes. It can be edited, but sometimes there’s a flicker when you move the mouse over the form, and it’s briefly displayed like this, shifted to the left, so clicking is complicated:

@Severin, the system will timeout when you have such long choices under the choices tab, which I see as follows:

list_name count
village 5290
arrondist 547
commune 78

You will need to use the external CSV file as used in these community posts discussed previously: