Apple has reportedly discovered a critical flaw in watchOS 2 and decided to withhold the update to fix it, pushing back today’s scheduled release. The issue may remind users of a similar predicament with HealthKit applications at the launch of iOS 8 last year.

Apple has not yet officially announced the new release date, but confirmed in a statement to 9to5Mac that the software will not come out today.

We have discovered a bug in development of watchOS 2 that is taking a bit longer to fix than we expected. We will not release watchOS 2 today but will shortly.

Users running the GM build of the software haven’t yet reported anything big enough to potentially stop the entire release, although there were some reports of sluggish performance throughout the beta. Many users have noted that iOS 9 suffers from the same performance issues on some devices, even newer iPhone hardware, so it’s unlikely that was the cause for this change of plans.

A source with knowledge of the issue told us this problem won’t impact the release of iOS 9 later today.