UPDATED | January 29, 2018:
Details about those reporting losses have been updated for accuracy. Since the original publication of this article, ETHNews has been made aware of another developer involved with Lightning who appears confident that the funds will ultimately be recovered.
ORIGINAL | January 26, 2018:
With the Lightning Network now available to be run on the Bitcoin mainnet, two Twitter users, one of whom is a Lightening developer, reported losing bitcoin as a result of one or more bugs related to the closing of payment channels.
ETHNews has previously written about payment channels and the Lightning Network in greater depth, but to put it simply, payment channels are (in Bitcoin's case) multi-signature wallets that allow two users to transfer value back and forth between them. The Lightning Network, which is still under development, is the web formed by connecting many payment channels together, which allows users to send funds to other users with whom they don't have a direct payment channel open.
Some members of the bitcoin community view the network as one of the blockchain's best hopes for being transformed from an environment containing speculative cryptocurrencies into a platform supporting payments (or micropayments) between potentially millions of users.
Several Lightning insiders, including the user of a reddit account ostensibly belonging to Lightning Labs CTO Olaoluwa Osuntokun, have cautioned the public not to run the network on the mainnet until further notice, but some eager bitcoin enthusiasts have disregarded these warnings.
At press time, a Lightning Network mainnet explorer indicated that these users, as well as Lightning developers, were running over 750 channels between 260 nodes, with upwards of 3.6 bitcoin loaded into the network.
It's not clear when exactly this second layer machinery will be free of the bugs that caused the funds to be lost, but for now, the Lightning team seemingly wants to develop it in peace, free from the distractions caused by uninvited users' activity on the network.