Earlier this week, Apple released watchOS version 3.1.1 as an upgrade, but it immediately set off alarm bells with users who complained that the software was faulty. After downloading the software, watch owners said their watch screens would display a red exclamation mark and direct them to Apple’s Help page.

That page recommended that users restart their watches by pressing and holding the side button and crown for 10 seconds. If the restart fails to fix the problem, Apple (AAPL) asks users to contact customer service.

According to users who discussed their problems online, the restart doesn’t work, forcing them to take their watches to Apple Stores and have them shipped out for repair.

Get Data Sheet, Fortune’s technology newsletter

Apparently after hearing about the problems, Apple this week suspended the availability of its software update. The most recent stable version is watchOS 3.1.

Apple released its watchOS 3 earlier this year to improve how quickly apps load, as well as tweaks to make finding third-party apps easier. Apple’s watchOS 3.1.1 was a minor update that included some bug fixes and added new emoji.

Apple tests its software updates with users before broader releases to find any flaws. However, some bugs can sometimes slip through the cracks, which apparently happened this time around with watchOS 3.1.1.

For more about Apple Watch, watch:

According to reports, including one from Apple-tracking site AppleInsider, which earlier reported the news about the software flaw, the bug is more likely to occur on Apple Watch Series 2 that were released this year. Older models don’t appear to be as susceptible to the problem.

Exactly why watchOS 3.1.1 has caused some Apple Watch units to have problems is unknown, and Apple hasn’t yet commented on its decision to pull the update. The company also did not respond to a Fortune request for comment.