Well, there are a few. Obviously, the fraud is probably gonna be people's main concern when considering LN. Also, there's the case of loss of decentralization, as funds are concentrated in certain nodes of the network, this is what facilitates faster transactions.
I don't know where is the central part of the Bitcoin Lightning Network? This is not accurate !! The Bitcoin Lightning Network is a temporary record between two parties who conduct many transactions without being recorded on the public Bitcoin Blockchain so that the transactions are processed faster and the final result is recorded only on the Blockchain, do you see there is any centralization in this?
An offline stance could also bring down the network. Taylor from Dash said the biggest issue with Lightning Network is “increased centralization” by concentrating funds in certain nodes within its network. In practical terms, this translates to a lock-up of user funds if one of Lightning Network’s nodes goes offline. “One server outage could feasibly cause disruption across the entire network, and it could cause a large number of users to have their funds frozen for days,” Dash said.
Source:
https://www.investopedia.com/tech/bitcoin-lightning-network-problems/The Lightning Network was found to be more centralized than initially believed, increasingly relying on hubs through a core-periphery model observed by researchers. The Lightning Network's (LN) configuration is becoming increasingly centralized, with multiple hubs being formed.
Source:
https://cointelegraph.com/news/bitcoins-lightning-network-found-more-centralized-than-expected-by-researchersThis is due to the network being too reliant on nodes with concentrated funds, which tends to give it "a degree of centralization", which is absent in the current blockchain implementation. This may make the network vulnerable to network-split attacks, which can occur in Proof-of-Work networks such as Bitcoin.
Bitcoin network (blockchain) essentially functions as follow, the miners are given, essentially a sum to compute, and the faster the nodes can compute that sum, obviously that depends on their hashing power, the faster a block gets generated and processed. Bitcoin uses the Hashcash algorithm for this. Difficulty and complexity of the sums gets more complex as the blocks get generated. A network split attack would essentially split the connection between two nodes, which, if performed on the nodes on which the network is too reliant, may cause transactions to be incomplete.
