Airplanes wouldn't be able to land. Power plants would shut down. Those were just some of the dire predictions faced by computer programmers and users worldwide as the year 2000 approached. In the end, the millennium bug that was widely expected to create computer chaos turned out to be more of a punch line to jokes than an actual problem.

Two decades later, the crypto world could be facing its own Y2K moment, when the Ethereum network undergoes a major software upgrade in September. The revamp, known as "the merge," is being billed as a seamless transition that shouldn't be noticeable to users of the most commercially important blockchain. Not everyone is convinced, especially when it comes to the more than 3,400 active distributed applications that are built on the platform.

"You know there will be those edge cases that will be interesting and exploitable," said Toby Lewis, CEO of Novum Insights, a crypto analytics provider. "One thing I can guarantee: It's going to be a very bumpy ride."