Problem with return?

Question

C++ / C#

This method weighs on the character

void OnTriggerEnter2D(Collider2D col)
    {
        if (col.gameObject.name == "set5")
        {
            if (wer == 4)
            {
                wer--;
                return;
            }
            if (wer == 3)
            {
                wer--;
            }
            if (wer != 4 || wer != 3)
                wer = 5;
        }
        if (col.gameObject.name == "wall3")
        {
            if (wer == 5)
            {
                wer--;
                return;
            }
            if (wer == 1)
                SceneManager.LoadScene("Level4");
            if (wer != 5 || wer != 1)
                wer = 5;
        }
        if (col.gameObject.name == "wall4")
        {
            if (wer == 2)
            {
                wer--;
                return;
            }
            if (wer != 2)
                wer = 5;
        }
    }

And there is such a problem. Here

if (wer == 5)
            {
                wer--;
                return;
            }

return does not always end the execution of a method. That is, approximately with a chance of 2:10 (I did not reveal the exact pattern), the method continues. And here

if (wer == 4)
            {
                wer--;
                return;
            }

return doesn't work at all and the method continues on.
I understand that there will be similar problems here.

if (wer == 2)
            {
                wer--;
                return;
            }

What could be the problem and how can it be fixed?
PS Do not blame me if I'm stupid and poorly studied (or understood) return. I work with return for the first time.