It is strange that such technical problems occur because I did not know any change that have happened in ADA network, but it may be tampering in the worst case (your funds are safe.)
According to what Bithumb announced on December 16, 2020, Cardano (ADA) deposits were disabled because that coin had an announced hard fork. Is it possible that they have not been able to adjust since then, or were there some more unforeseen difficulties around the hard fork that still affect deposits, only they know. Someone said that crypto exchange lost its reputation a long time ago, because if you are hacked as many as 3 times, the only question is when it will happen again.
Due to the blockchain hard fork of the Cardano (ADA), deposit and withdrawal services of ADA will be suspended. As soon as the ADA network is stable, we will resume deposit and withdrawal services.