Basically my question boils down to are they constantly growing and need staff, or is it a rough place to work at and they have lots of turnover? I'm interested in applying but kind of want to know more.
In my eyes, it's a red flag and not a great sign. If a company treats people fairly and pays market rates, the job listing is unlikely to stay open very long.
At the same time, a red flag is just that - a signal, not damning proof of anything untoward.