almost all exchanges have issues like this at times like this!
whenever there is a big drop that many people sell or whenever there is a recovery (like now) when all those people and more come back to buy back bitcoin these exchange servers can not handle this much customer and become slower and even go down sometimes. and that is something that we can't do anything about.
even if you switch to other exchanges like Kraken,... you will see the same problem at some point.