It's not a bug. It's them running A/B tests to completely block mobile users that aren't on the app. They've been implementing different versions of this for over a year now. They always lie about what it was. Actually they pretty much habitually lie about all of their tests and changes.
I got this bug on desktop, running chrome, with no VPN.
This was, as most things like this are, just a pure dumb fuck-up by some guy putting things on prod without properly testing and staging. No need to put on any more tin foil hats than we already have, the incompetence is plenty reason enough to point and laugh.
If an internet corporation has a history of enshittification, it gets increasingly hard to clock up these kind of things to incompetence. While stupidity can certainly explain some things, it's usually safe to assume it's a bit of both