Updated

Apple Inc. acknowledged problems with cellular connectivity in its newest smartwatch, raising questions about the device’s most significant feature days before it goes on sale in stores in the U.S. and other countries.

In a statement Wednesday, Apple said the problem connecting to cellular networks occurs when the Apple Watch Series 3—the first watch from Apple to feature an LTE chip for cellular service—joins “unauthenticated Wi-Fi wireless networks without connectivity.” Apple said it is “investigating a fix for a future software release.”

Apple issued the statement after reviewers from The Wall Street Journal and the Verge encountered problems at times making calls, connecting with the Siri virtual assistant and maintaining a cellular-network connection. The Journal ran into issues across multiple wireless carriers.

Reviews from the New York Times, USA Today and other outlets didn’t report significant issues with calls and connectivity. A spokeswoman for T-Mobile US Inc. said it tested the watch extensively and it “performed well” on the company’s network. AT&T Inc. referred questions about the issues to Apple.

This story originally appeared in The Wall Street Journal.