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.

Specifically, Reagan made a point to cut our nose to spite our face just to not pay ATC workers more money. For political and Ideological reasons.

So why the fuck would any talented individual choose to go work for the "Get an example made out of you" department, on top of the horrific stress of the actual job!?

The idea of a union that "isn't allowed" to strike is a joke. Next will be a union that has a max membership of 1!