Running powershell script to perform automated webpage login from task schedular behaves differently from running the script manually

My university requires all computers to perform a web-based login in order to get-access to the internet, and claims that all users will log-off automatically in the mid-night (sounds strange, but it is true), so I am trying to write a powershell script (in Windows 10) to perform automatic login at mid-night.

My script is list here. It opens an IE process in the background (in a nonvisible way), fill in the username and password, login, and kills the IE process.

# If there are existing Internet Explorer processes, close it
$IE_Process = Get-Process iexplore -ErrorAction Ignore
if ($IE_Process) { 
    $IE_Close = Foreach-Object { $IE_Process.CloseMainWindow() } 
}

Stop-Process -Name "iexplore" -ErrorAction Ignore

# Login Information
$url = "http://xxx.xxx.xxx.xxx/"
$username = "xxxxxxxx" 
$password = "xxxxxxxx" 

# Open an IE process
$ie = New-Object -com internetexplorer.application; 
$ie.silent = $true 
$ie.navigate($url); 
while ($ie.Busy -eq $true) 
{ 
    Start-Sleep -s 1; 
} 

# The stupid webpage needs to submit twice
$ie.Document.getElementById("loginname").value = $username 
$ie.Document.getElementByID("password").value = $password 
$ie.Document.getElementById("button").Click()
Start-Sleep -s 1; 
$ie.Document.getElementById("loginname").value = $username 
$ie.Document.getElementByID("password").value = $password 
$ie.Document.getElementById("button").Click()

# Close the IE process
$IE_Process = Get-Process iexplore -ErrorAction Ignore
if ($IE_Process) { 
    $IE_Close = Foreach-Object { $IE_Process.CloseMainWindow() } 
}

Stop-Process -Name "iexplore" -ErrorAction Ignore

Remove-Variable -Name ie,username,password,url,IE_Process -ErrorAction Ignore

The script is saved as "login_IE.ps1". It may be poorly written as I am new to powershell, but it works. If I open an cmd window and execute the following command, I am logged in.

C:\WINDOWS\system32\WindowsPowerShell\v1.0\powershell.exe -ExecutionPolicy RemoteSigned -File C:\Users\MyName\Documents\Powershell\login_IE.ps1

However, if I create a scheduled task in windows task scheduler executing this script, it doesn't work. I fill the "Program/script:" as:

C:\WINDOWS\system32\WindowsPowerShell\v1.0\powershell.exe

and fill the "Add arguments (optional):" as:

-ExecutionPolicy RemoteSigned -File C:\Users\MyName\Documents\Powershell\login_IE.ps1

The scheduled task is run under my account (I am the only user of this computer).

If I run the scheduled task manually, in the task manager I can see two IE process opened in the "Background process", communicate with the internet, and then get killed, so I am pretty sure that the script has actually been executed. But I found I am not logged in since I don't have internet access, where could the problem be?

Any advice is really appreciated. Thanks in advance.