If there are two file fields, the files are not sent

I have a simple form,

The form has two checkbox fields, if each one is selected, this enables the file field that corresponds to each checkbox.

If I check only one checkbox field, one file field is enabled and the form sends it without problem, and if I do it with the other checkbox field, only the second file field is enabled and sends it without problem.

But if I mark the two checkbox fields at the same time and attach the two file fields, the form is sent, but none of the attached files or the file upload URL arrive in the email. as if no files were selected in either of the two file fields.

How can this be fixed?

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