I am wondering if the tech removed the antibacklash spring when servicing and forgot to put it back in? They pop out very easily but I don't know if normal servicing would mandate removal of the antibacklash spring from the bobbin case. Additionally I believe a magic genie bobbin washer would cover up the antibacklash spring and defeat the purpose of it. I don't think you are supposed to use both at the same time but I could be wrong. I do know you have to remove the antibacklash spring when using magnaglide bobbins. I have only had backlash on a few occasions and that was when using the cardboard prewounds, like the ones Superior sells. I rarely use them anymore.
I pretty much use magnaglide prewound bobbins exclusively and never have a problem with backlash and rarely have issues with tension. To me they are well worth the extra expense.