The only thing I can assume is:
They have a target of minimum profit/overhead cost that they are required to operate per each user. So in the first place, that is why they set up the minimum deposit requirement. Therefore, speaking about your cases, because of the current situation, your amount is low enough that they might be didn't simply care enough about it since solving the cases would outweigh the cost instead of the benefit (time = money).
Also, maybe they didn't have any automated process to solve these particular cases. Developing it would also require some cost and time to develop it.
Maybe you are right, But i expect a big exchange like Huobi should not have this kind of issue. This exchange is popular and also have thier own blockchain.
This will make me think that thier blockchain might not be safe enough and can even be a centralised shitchain. I was so disappointed by not seeing my remaining 39 matic added because i dont except an exchange like Huobi to hold customer's coins and not add it to thier account.