The needles that came with the machine have 1/2 stamped on them. They're similar to 15x1 needles, but I think the cone shape on the top of current made ones makes the eye line up differently. I don't know why the 1/2 needles work, but they do. I don't have any non e machines like treadles etc. so have never had issues with needles not working correctly as any machine I've ever owned used 15x1 with no problems.
I don't think there's anything wrong with the machine or that it's been fiddled with. I suspect it needs specific needles:<