As far as I know, not in a way that an autonomous driver can't overcome but a human can. I'm speculating a lot, but if I had to say why driving (fast) on dirt

As far as I know, not in a way that an autonomous driver can't overcome but a human can. I'm speculating a lot, but if I had to say why driving (fast) on dirt is substantively more complex than driving on tarmac for an AI, it's because road conditions change much more rapidly on dirt. You're expecting to be constantly in various states of intentional traction loss (sliding), including having a few or all wheels off the ground with some frequency (jumps). If you're driving slowly enough to maintain proper traction, then there really isn't an issue. But if you're rallying down an Argentinian mountain trail (take a look at some WRC on-board recordings on Youtube for an idea), you'll have an extremely challenging planning problem. I don't think it's insurmountable for AI, it's just that racing over dirt has a lot of nuances especially to car handling that you never have to deal with on tarmac because good tarmac racing involves basically 0 traction loss and smooth, static surfaces. Not that tarmac racing is easier... where the track is simpler, you make up for it in sheer speed and the complexity of having to share a track.