Tried it but for me it also shows "address not found".

I would say that it's not concerning, but you also said: "I do no longer find the address I sent btc to on the ICO list."

I have no doubt that they'll fix it but it seems to be more then just a technical-issue then. First I believed it's maybe just your browser - but if your BTC doesn't even show up anymore, you should get in touch with them.

It is a bit worrying, considering it did work earlier. However I do have the Privkey and everything, hopefully they have not deleted me and taken my BTC

If that should be the case it would be something like "human-mistake" and they would fix that. Your transaction is still on the blockchain etc. It's just guessing because I have no idea, but let's say somebody claimed his BTC back and they took the wrong address out or something like that.

I doubt that it's about that, but whatever happened it can be figured out what went wrong.

I don't believe that you did something wrong. If your BTC-deposit/ICO-address is not even to find here: https://www.antshares.org/ICO/HeroList

...it's kind of mysterious.

What you should provide to them is your ANS-address and your BTC-ICO-address. 

I just followed the transactions of the ICO to this address: https://blockchain.info/de/address/3Q8pgRFtxbUp8wtGbtQqRNXPs1B4i6enu1

Still    6,119.319402 BTC on it.

Everything works now. Hopefully it was just a technical error. Thank you guys who tried to help me out!

Yes they are chinese based but half of there ICO investors are from rest of world and half from china.The devs look highly professional so you should'nt be worried where the coin originates

What is the relationship between OnChain and Antshares?

This coin looks like it's going to be big next year. I'll keep it in my sight.

There's a big spike in the trading volume in Yuanbao in the last 24hrs, around $40K ANS were traded in IOUs, I wonder where it came from!