How to fix "Incorrect server response" error?

Question

1C-Bitrix

When uploading any file up to about 5 MB to any element of the infoblock, the error "Incorrect server response" occurs. On machines with Windows OS, the problem appears extremely rarely, on Linux - almost constantly.
I contacted Bitrix technical support, who was able to identify the problem in /bitrix/modules/main/tools/upload.php

$receiver = new \Bitrix\Main\UI\FileInputReceiver($_POST, $_POST["signature"]);

returns an empty POST for small files. Bitrix advised to contact the hoster. The hoster could not identify the problem. Bitrix technical support has also merged.
Actually now it is time to turn to the forums. Can anyone suggest anything about solving the problem?

Answer 1

The problem was that at one time the site created a ServiceWorker to display the page without an internet connection. This service worker loaded a bunch of left files and previous $_POST files in the background. the error was knocked out precisely because $_POST['signature'] == NULL. That is why resetting the page cache allowed the file to be loaded.
I solved the problem by simply disabling the ServiceWorker for the admin part.