United Airlines says a technology issue has been resolved after grounding flights nationwide Wednesday—but disruptions are ongoing and delays are expected into the night.

An undisclosed “technology issue” has grounded United Airlines flights across the U.S. United Airlines said in a statement Wednesday that flights on major routes were being held at their departure airports because of a technology issue.

Around 35% of the carrier’s scheduled flights faced delays on Wednesday night, while 4% were cancelled as the airline faced the residual impact of a technical snag.