Same observations here. Except if they worked in software during their undergrad (as an intern for example) or minored in CS and majored in something else.
Undergrad in CS and a Masters is also typically not a red flag.
I'm also in Australia and have found your perspective to be identical to mine.
Unrelated undergrad + IT/CS Masters usually equals "I want money" or "X was terrible so I'm falling back to something safe". Obviously, that's not always the case, but it has been in many interviews (and a few hires).
When kids ask about undergrad I say, 'Do a degree called "software engineering" if there is one, otherwise "computer science" is the same thing'. Some unis just have one general coding degree and pick the name randomly out of those two, some have both with either an industry or research focus respectively.
eg in my CS undergrad degree I got some theoretical & research stuff (simulations and queuing models, computer vision being two of the research focus areas), but also some good old Operating Systems, compilers, databases, practical programming, software engineering, etc. Vocational stuff; has been very useful!
Masters students (back then at my uni, and seemingly now too) mostly wrote essays and had the option of doing very, very little coding at all.
I've been hiring engineers for a few years, and I've come to associate a CS/IT Masters + unrelated undergrad with bad candidates and generally use it to filter _out_ candidates (unless something else on the resume catches my eye). Conversely someone with a science degree and a bit of experience (or some decent personal projects for fresh career-switchers) is a much better sign.
My experience (read: anecdata, opinion, bias) is that the IT/CS masters candidates I've interviewed have switched for money and because of failure-to-thrive in their original industry, and have no care or passion for software, and have done poorly on interviews. The non-CS-undergrads-but-no-masters candidates are just the normal spectrum, with a higher variance (some with 0 skills but much hope, some with really interesting backgrounds and wide-ranging interests like how you sound).
Data disclaimer: I'm only at ~500 total lifetime interviews/10 years experience so far, I'm in Australia, I have no recorded numbers or hard data just "feelings" and "intuition".