Selenium C# - driver "pause" , open new form and get data from it, continue driver and paste data

I'm having problem with Selenium driver, because it freezes my form which contains crucial data for the rest of the task.

Here is part of the code where problem occurs :

            element.SendKeys(OpenQA.Selenium.Keys.Enter);
            SendKeys.Send("{TAB}");
            driver.Manage().Timeouts().SetScriptTimeout(TimeSpan.FromSeconds(15));
            MainForm FormN = new MainForm();
            FormN.Show();

It freezes here and it skips PerformClick(); action and proceeds to "FindElement(By.Id..."

            FormN.btnCopy.PerformClick();
            FormN.Close();
            driver.FindElement(By.Id("twofactorcode_entry")).Click();

I already tried : async, sleep, ImplicitlyWait etc.

Note : When driver finished the task, then form loads normally.