[shka]

One of the changes from php 7.1 => 7.2 http://php.net/manual/en/migration72.incompatible.php
Warn when counting non-countable types
An E_WARNING will now be emitted when attempting to count() non-countable types (this includes the sizeof() alias function).

Try

PHP Code:

        if ( is_array($this->callbacks) || $this->callbacks instanceof Countable )
        {
            foreach ($this->callbacks AS $callback)
            {
                call_user_func($callback);
            }

            unset($this->callbacks);
        } 


In php 7.3 there will be a is_countable() function. https://wiki.php.net/rfc/is-countable

But vB4 isn't compatible with php7.2. So this will be only the starting point of a never ending error-solution-error-warning-error...circle. Go back to 7.1 if possible.