Canadians travelling to the US experience mass delays due to "system outage"

It’s been quite the morning for passengers as an outage in the US has caused massive delays in Canadian airports, especially on the east coast.
On January 11, the Federal Aviation Administration (FAA) stated that it was working to restore its Notice to Air Missions System.
“We are performing final validation checks and reloading the system now. Operations across the National Airspace System are affected,” reads the tweet. “We will provide frequent updates as we make progress.”
The FAA is working to restore its Notice to Air Missions System. We are performing final validation checks and reloading the system now.
Operations across the National Airspace System are affected.
We will provide frequent updates as we make progress.
— The FAA ✈️ (@FAANews) January 11, 2023
The outage has caused delays for US-bound flights mostly on the east coast of Canada, with Toronto Pearson Airport advising passengers to “check the status of their flight before heading to the airport.”
Given an FAA system outage, we advise all US-bound passengers to check the status of their flight before heading to the airport. https://t.co/8EcwDAKGfG
— Toronto Pearson (@TorontoPearson) January 11, 2023
In Montreal, several flights headed to the US are also delayed.
According to an FAA update, normal air traffic is “resuming gradually” and the ground stop has been lifted.
“We continue to look into the cause of the initial problem,” they stated.
Update 5: Normal air traffic operations are resuming gradually across the U.S. following an overnight outage to the Notice to Air Missions system that provides safety info to flight crews. The ground stop has been lifted.
We continue to look into the cause of the initial problem
— The FAA ✈️ (@FAANews) January 11, 2023