Some users in countries including Singapore, Malaysia and the Philippines were still reporting problems using the app more than 24 hours since outages started occurring.

Grab, preparing to go public in one of the largest special purpose acquisition company (SPAC) mergers, said an issue with a planned system upgrade had caused the disruptions. “Core services” have been restored, though some users may still have trouble with the app, it said.

“Our core services have been up and running since late yesterday morning, and our users and partners have been able to use Grab services per normal,” the company said in a statement.

“However, a small segment may still experience minor issues as we work on completing the upgrade. We’re sorry for any inconvenience caused, and are communicating with our partners who have been affected to ensure full support to them.”

Millions of people across Southeast Asia rely on Grab for car and scooter rides as well as meal deliveries and digital financial services.

The service disruption comes just weeks before the Singapore-based company is preparing to merge with Altimeter Growth Corp, the US special purpose acquisition company of Brad Gerstner’s Altimeter Capital Management.

Grab has postponed the US$40 billion deal – announced in April and one of the largest-ever mergers with a SPAC – to the fourth quarter as it works on an audit of the past three years’ accounts. The company reiterated last week it expects the deal to complete this quarter.

Grab operates in more than 400 cities in eight countries in Southeast Asia. It is the dominant player in the region of about 650 million people, though competition is intensifying from rivals such as Gojek, which merged with e-commerce company PT Tokopedia to bulk up.

Grab is also competing against Delivery Hero SE’s Foodpanda and Deliveroo Plc as well as new entrants such as AirAsia Group Bhd in the region.