AND the last one was just found to be invalid.
24 seconds too late, apparently. Nothing in the pipe.

So a different pool or someone found the block 24 seconds before us?
Yep. It's about a 1.5% chance that a block will be orphaned, about 1 out of 67 blocks we find. The pool could toss out the orphaned block earlier, since noone ever chained to that block, but I suppose there's something to be said for holding out for a miracle.