php（wordpress） - 服务器无法响应文件更改

I'm facing weird problem which a bit complicated to understand. So the situation is that:

1. we have 2 installs (actually more, but not relevant for now)
2. both installs places on same server (apache + nginx)
3. we update our code and therefore deploy to staging - first install works great, second one has problem.
4. the code is 100% percent the same
5. there is no influence of other plugin (wordpress) on the specific part of code

The relevant code is the following:

$track  = new trackClass();
$track->store_parameters();
$parameters = unserialize($track->parameters);

class trackClass // this class sits on different file
{

    public $parameters;

    public function __construct() {
        ...
    }

    method...

    method...

    method ..

    public function store_parameters()
    {
        ...
    }

}

Before we modify our code, the function store_parameters was private, now its public.

So when on the second install the code is running its raise an error that the store_paramters() function is private and not accessible (remind you that it happens only on the second install).

I tried another thing get_class_methods($track) and the response was all the methods except the store_parameters(). Again - weird.

Next step, put wp_die('test') in the top of the file of the class. Refreshing the page and all as usual (the file is definitely loaded). If I try to access the admin (wp-admin) the changes make difference - the page is killed, blank screen and 'test' on it.

Next step, remove this file completely from the server. Refreshing the page and nothing happen. Their is ajax request from the class file which run as usual, like the file is exists and everything is ok. Again, going to the admin page and the error is raised (require_once ... not found).

Its doesn't seems like its code or development problem. The code is same. I'm afraid that its something on the server side / environment (apache, nginx) but unfortunately I've no access to the linux, I only can chat with the support of the hosting company.

They are insists that is code problem. No matter the tests I wrote above.

What can cause this kind of problem? I'm losing my mind here with no lead, its like the file is stuck somewhere.