Yes, many cases lose bitcoin and the amount is not small. Most of them are people who are less thorough with their wallet account. Eg 2fa is not activated, or due to other reasons that is exposed Phishing site Scam pages. Many modes are done by hackers to get Bitcoin. Therefore be careful in reading the website address and prepare 2fa on each of your Bitcoin wallet account. Be safety!

Some time ago a platform exchange could be hacked and causing defects to the property of the users. proving that everything can be hacked as well with bitcoin.

breaking into system bitcoin is very difficult because of its security that already developed, i also don't understand about security hidden from bitcoin. but bitcoin have developers own and team in the field of security.

In fact, Bitcoin is theoretically vulnerable to hacking due to its code is open source and programmer can be constantly reviewing it. There is one type of hacking which can successfully hacked bitcoin which called the 51 percent attack. Due to bitcoin is decentralized, bitcoin will be vulnerable if more than 50 percent of the computing power is being controlled by any one of the player. There is one case where a group of people has achieved control 50 percent of the bitcoin network's power. However, hacking bitcoin is not that easy. When you are controlling such huge percentage of the power, you computer must be really good and the electricity bill can be very high. And also the more the poeple using bitcoin, the larger the network, the harder for the people to hack in.

In terms of structure, anything that is designed and built can be brought down with disproportionate collapse, it just requires the correct approach and magnitude. The same for the cryptocurrency district too. Nothing is impenetrable. But why would you?

I think that everything can be hacked because if you are a good hacker and know what you are doing you can hack anything.
 Like even big companies have been tried to hack by guys and some of the attacks worked.

Bitcoin has a weak spot according to Satoshi Namakoto himself,  you will need alot of CPU computing power to do so.  There are bad node and good nodes, all the attacker has to do is pull out more power to construct a faster malicious block chain where the BTCs spent by the attacker are immediately sent back to him by the recipient and then double-spent among multiple recipients.

Even if any software is hackable, I have not seen any blockchain hacked. The only things that get hack are for now the smart contracts on top of the blockchain. Does anyone know if any crowded blockchain had been hacked?

Nothing is safe from hacking, and Bitcoin isn't an exception, not at all. It's just that it isn't exactly easy to perform such an action, and it isn't possible to destabilize the entire bitcoin economy by doing that. You are safe if you know what you're doing, and your pockets are safe even if you don't act irresponsibly with your stash.

Hacking is an art and there is nothing impossible for an hacker. All things on internet is hackable. While dealing with bitcoin it is our major priority to focus on ensuring authentication and using cold storage wallets or ledger wallet or Nano S Wallet. Also block chain is one of the best platform for storing our funds as it is like a gate, every 10 minutes a new gate is created, so hacker needs a new gate to hack our bitcoin, if they fail a new gate is created.