Olise was a huge loss, not sure what the thinking was behind selling Andersen either, he was good for them. I don't know if he pushed for the move or what, it did seem kind of sideways for him at the time. To be fair, they're still not too bad at the back.
Was always that thing that some people said - outside of about 8 clubs everyone else is one bad season away from potential relegation. Perhaps not so much in recent years as the promoted clubs struggle so much to the financial gap and I think Palace will be ok ultimately. Easy to go from something like 9th to 17th and vice versa. Lose a key player, have a bad transfer window, get some injuries, appoint a bad manager etc.