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Long delays could mean they are preparing to refuse the application. I was called once by a student visa processing officer to provide more information as he was at the grant stage. I sent him the document and he asked me to call back after I have sent it. When I called, he looked up the general email for students and said he can only see 5 new emails. They do check emails and they choose not to answer you. If your student is from Vietnam, India, Philippines, Pakistan or a known hot spot, you can be sure that they will try to refuse. I also notice that students who are over 30 will be subjected to scrutiny as well. Average wages in these regions have very low yearly income earnings and with this reason alone, case officers can use it freely to refuse a visa.
I had the same problem with the Special Temporary Entry Centre in Hobart, waiting on a 402 nomination and visa application. After 4.5 months of emails getting no response (advertised processing standards 4 - 6 weeks) I lodged an online complaint form and had a result the following week. You might like to try this approach.