These are the absolute crappiest terminals on the market, and they're becoming the most-popular. The wires are (supposed to be) clamped into a serrated channel in the lead, but if the wire is too thin, there's not enough clamping force. And if there's too much wire (like this), the straps bend & weaken, reducing the clamping force. Also, with all the pockets & threads, they collect acid, causing rapid corrosion. And like all lead terminals, they stretch over time, even if they're not overtightened. But they're ALWAYS overtightened.
And that paint that makes them so popular is another BIG problem: it's usually allowed to coat both the wire channel AND the hole for the post, causing a poor connection in 2 places, even when new & clean. The connections only get worse as it ages. These were installed less than a month ago, and they've already failed (on Christmas day) which is why I'm replacing them today with solder-on terminals. Here's someone else's pic of a similar terminal:
Note that the interior bore is almost completely coated with highly-insulative PAINT, and that's probably the same reason the cable got hot enough to melt its insulation - paint in the cable pocket.