Authorities said they were working to address a technical fault which left the UAE's main coronavirus phone application unresponsive for several hours on Thursday.
The Al Hosn app showed error messages for many people.
The National Emergency Crisis and Disaster Management Authority apologised on social media.
"Work is currently under way to address the technical malfunction in the system. We apologise for the delay," Ncema said.
Government health portal Weqaya responded to messages on Twitter by urging users to update the app.
There is an existing workaround, posted to the Ministry of Health and Prevention's Facebook page in August last year, that explains how to retrieve your last PCR result.
Users experiencing unresolved problems with the app should email firstname.lastname@example.org, it said.
It was not clear if the issues were a result of a broader app update. According to the Apple store, Al Hosn was last updated on June 11.
Abu Dhabi residents must show their green status – meaning they are vaccinated or had a recent PCR test – on Al Hosn to enter most public places. These include malls, supermarkets, gyms, bars and restaurants.
The same app is used to show to police officers at the border from Dubai to Abu Dhabi.
On Thursday, some users found they could access a cached version of the status page to show they had green status before the fault occurred.
Security guards at malls were accepting a screenshot of these latest results, staff from The National found.