It sounds like you have a wiring connection in the wall that went bad, most likely between your last working light and the first non-working light. Unfortuneatly if the wiring is buried in the wall you have to ask yourself how much you like your lights and try to access the wiring. Something else you may check but probably won't end up being the problem is the switching. Sometimes multiple switch legs are ran from the switching location and maybe you have a bad connection in your switchbox. Hope this helped good luck!

While a loose wire is possible, it's also possible that the LV power supply feeding certain fixtures (if there is more than one) has taken a dump for some reason. I've seen that.

Thank you for the follow-ups.

I do have a question, though: what does it mean for a power supply to "take a dump"? And what can I do about it?

It means it's failed for some reason. You'll have to replace it if it did. It's rather easy to check. If there's power in the primary side and nothing on the output side, then it's gone.

... Okay, we have the "bad wiring inside the wall" post... So I suppose the OP must have squirrels or rabbits or something living in there to eat at the wires...

... what's missing is the far-more-likely "Bad connection, either at the last working light, or at the first non-working light" post.