Shamrock Shakes are back on the McDonald's menu this week, but at some restaurants the seasonal treat relies on a machine with questionable reliability.

Why it matters: The Shamrock Shake and Oreo Shamrock McFlurry use a soft serve ice cream machine model that reportedly breaks so frequently that a data engineer built a website to track defective devices. The problem has sparked hacks and lawsuits.

The intrigue: Even the Chicago-based fast-food giant has been self-deprecating about the issue.

Catch up fast: Rockton-based Taylor Company has for decades manufactured the machines that have drawn complaints nationwide, but a spokesperson for McDonald's says it's not the company's only manufacturer.

• Taylor mechanics are the only ones who know how to fix their machines when they break, Wired reports. A spokesperson declined to respond to Axios' question about the issue.

Flashback: A company called Kytch made a gadget that could hack Taylor machines and potentially diagnose the problem. Beginning in 2019, the founders began trying to sell it to franchisees.

• But in 2022, Kytch filed a lawsuit alleging McDonald's sent communication to every U.S. franchisee accusing Kytch's product of being unsafe and prone to cause "serious human injury," which crippled the three-person startup.
• McDonald's would not respond to Axios' questions about the ongoing lawsuit.

What they're saying: "Our sales data across the past couple years has shown our shake machines are up and running around 95% of the time across the country, depending on the local restaurant," a McDonald's spokesperson tells Axios.

• "We're working to bring that number as close to 100% as possible by providing additional training resources for crew members and regular maintenance 'check-ups' to keep our machines running smoothly."