You'd probably be interested in their set of slides on techniques for constructing robust software [1]. It talks about this issue, among others. For one thing, the processors could easily be in different states due to resources each has access to, so the same code could behave differently on different processors. Another topic they touch on in the slides is the notion of having multiple implementations of the same program, with compatible inputs and outputs but different implementations written by different teams that did not communicate.

[1] https://www.fastonline.it/sites/default/files/2019-06/Robust... (I couldn't find a version on the stratus website any more, but this appears to be the same as the one I downloaded from their site many years ago).