There are no responses or messages, neither in the console nor on the display, and not even in the logs. Where to look to decide?

Question

Yii

There is a site on Yii2.
One of the pages has a form that the user submits.
In this form, there is an upload of two files in docx format.
When submitting the form, more than 13 folders are created on the server in which these two files are uploaded (each folder has a copy of these files).
It also creates more than 13 records in the database.
After that, a message about the successful submission of the form should appear on the user's screen.

It's as it should be, BUT no messages appear.
There is nothing in the Yii debugger either.
Nothing in the browser console either.
And at the same time, if no more than 12 folders and 12 records in the database are created, then messages appear.

I don't even know where to look to understand what's going on.
Therefore, I will be very grateful for any thought towards solving this mysticism.