Why would there be? Pluribus doesn't issue security clearances, the customer agency (in this case the NSA) does. It would be up to the NSA to do any additional background checks/vetting/polygraphs regarding security clearance for any contractors. Working for a contractor/switching jobs is hardly suspicious activity, so the NSA would have no reason to investigate her. Likewise Pluribus had no reason to be suspicious, so the most they'd do beyond the standard corporate background check is call up the NSA to confirm her clearance was active. At the end of the day even the NSA doesn't have the resources to be constantly vetting 100,000+ employees and contractors.

There are things that can easily be detected and cause you to have issues with a clearance. For example, if you get arrested or have other significant legal issues, someone will probably find out. Also, if you stop paying your bills long enough to have severe credit issues, someone will likely find out about that too.

For social media activity, someone would likely have to report you for anyone to take action.

I for one think its pretty reasonable, it sucks working for the government enough already, if we put people under 24x7 surveillance just for trying to serve their country they will go from having very few talented/ethical people working for them to absolutely none.