> I'm not sure if they were the only controller working at the time, they continued working after the incident which seems unusual; my understanding is normally they'd be relieved by another controller

I remember late last year, couple of months ago, US ATC controllers were without pay but forced to work anyways (similar to TSA I suppose, although I don't think they were forced, but volunteered to work without salary), is that still the situation? Couldn't find any updates about that the situation been resolved, nor any updates that it's ongoing, if so though it feels like it'd be related to the amount of available controllers.

ATCs weren't exactly forced to work: they aren't slaves and are free to quit any time. But if they didn't show up for assigned shifts even though they weren't getting paid then they were subject to disciplinary action including termination. Some of them called in sick, or took on temporary second jobs to bring in some cash (obviously a bad thing from a fatigue management standpoint). After the government shutdown they were paid in arrears for all of the hours they worked. It's crazy that Congress plays political games with essential services like ATC.

The US has had trouble keeping enough controllers. It's a skilled but extremely stressful job, and so retention would always be difficult but the US also works hard to make it suck more than it should, and of course the over-work from not having enough people makes that even worse.

But no, AIUI only things that were somehow deemed part of "Homeland Security" are frozen, the TSA are part of Homeland Security but the ATC are under the FAA. So this particular partial government funding lapse wasn't causal, at least directly.