I agree, the second crash is pretty surprising and might indicate that there is much that is not known about the problem. The pilots reported that they could not trust any instruments, so it was much more complex than the clean MCAS scenario that we have considered so far. Cascades of errors are common in the failure of software systems as the first failure can put the system outside of the testing envelope. From following this thread it looks like the MAX had a glass cockpit (screens instead of analog gauges) that the other models did not have, is that correct? I have actually done almost exactly that sort of programming and it is not as simple as it sounds.
Both planes were (according to media reports) practically brand new which should mean that they were pretty close in the production line. That is kind of a scary fact on its own.