@Slyph People do that, because people are stupid. Thibault had a talk about this at some convention, about how he had to severely limit basically anything, because many ppl did stuff like trying to import thousands of thousand move games and hitting "Computer Analysis" on all of them, killing the servers.
There is something "wrong" with your FEN, namely that it starts at move 124.
5k2/8/1r6/5PKR/8/8/8/8 b - - 0 124 <- this is what you imported.
5k2/8/1r6/5PKR/8/8/8/8 b - - 0 149 <- this will cause the engine to resign after 1 move
5k2/8/1r6/5PKR/8/8/8/8 b - - 0 <- import this instead (as you see, no move number at the end), and it'll work properly.
This is technically a bug (it should go by the movecount /played/, ie 28 in your game, rather than the movecount /displayed/, but since it's such a niche issue to occur, I dunno if it warrants much of a report.