cause and effect will always be the same
Actually no. Mostly, but some actions affect the PRNG and when loading saves they haven’t remembered to reset the effect of those, so the results can change a bit between loads. It has been a while, so I don’t remember the specifics. But you can abuse this property to get out of really tough spots by gaming the PRNG across loads.
I have probably save scummed too much.
I hate the PRNG of XCOMs. For anyone suffering from that I recommend Hard West. It’s a buggy game, but the luck mechanism is interesting. Basically when missing, your luck increases, and eventually that helps you hit. So missing a good shot isn’t that bad, because you can build a strategy on it regardless.