Computable versions of AIXI (such as AIXItl) also fail to find themselves in most situations, as they generally can't simulate themselves.

That is the same as any other computable agent, surely. No agent can handle the infinite recursion of an agent simulating itself, simulating itself, simulating itself...

Real agents typically have incomplete models of themselves. That's perfectly good enough to learn that bashing yourself on the head gives you a headache. Babies typically learn such things at a young age.