Based on your description, it seems like you are experiencing an issue with sending headers after outputting content in PHP.

The error message 'Warning: Cannot modify header information - headers already sent (output started at /path/to/your/file.php on line X)' typically occurs when there is some sort of output being sent to the browser before your `header()` function tries to send a new HTTP Header. This can be caused by:

1. Outputting any kind of content, whether it's an HTML tag or even just a space character (even if it's inside another file that gets included) before calling `header()`

2. Your PHP script is throwing notices or warnings before you call your header function.

To fix this issue, make sure there are no spaces at the beginning of any of your files and also turn off error reporting in your php.ini to prevent these kind of messages from being displayed on production servers:

```php

error_reporting(E_ALL & ~E_NOTICE);

```

You can also use `ob_start()` function before including all necessary .php files so that everything will be stored in a buffer instead of getting sent directly out to the browser.

Also, make sure you're not calling any functions like `header()`, `exit()`, etc. after output has already been sent using ob_end_output();

Here is an example:

```php

ob_start(); // Start output buffering

// Include all necessary .php files here...

// Call your header function only if it hasn't been called yet...

if (!already_header_sent()) {

header('Location: some-page.php');

}

// ... rest of the code ...

ob_end_output(); // End output buffering

```

As for why this only happens when you refresh the page, it's probably because after each request PHP starts fresh with no variables or settings carried over from previous requests. So if there was something causing output to be sent before your `header()` call on one request (for example a notice being thrown by another script included later in the include chain), that wouldn't affect subsequent requests unless they also triggered whatever caused it again.

Hope this helps! Let me know if you have any other questions.

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