The phrase "a troubling instance" is correct and usable in written English.
You can use it to describe a specific situation or example that raises concern or discomfort.
Example: "The report highlighted a troubling instance of negligence that could have serious consequences for public safety."
Alternatives: "a concerning example" or "a disturbing case."
Earlier this month in Insurance Liability Project Exemplifies American Law Institute's Mission Drift, we discussed an especially troubling instance of where the American Law Institute (ALI), a private organization known for its "Restatements" of common law in areas such as torts, products liability, and contracts, was instead revising the law.
This is a troubling case.
The most troubling instance of that in the current report is a manufacturer that uses a fiberglass flame barrier with organohalogen flame retardants and the heavy metal antimony.
Whatever the reason Google was experimenting with harvesting Android users' location info, it's another troubling instance of the company slurping up sensitive user data without making people explicitly aware it's doing so — let alone giving users controls to opt out of another major invasion of their privacy.
But there are troubling instances in which an undisclosed financial tie has created after-the-fact problems for substantial research projects.
In the past six years there have been several troubling instances of influenza viruses that leapt directly from birds into humans.
Testing is done in meat-production facilities, but Mr. Moss found troubling instances when slaughterhouses refused to sell their meat to producers or companies that wanted to do extra testing for the particularly dangerous E. coli that paralyzed Ms. Smith.
Beyond facial recognition, there are other troubling instances with real-world implications.
But there are too many troubling instances in which bigots prove incorrigible.
It's worth noting that some of the most troubling instances of violence have happened in cities -- Portland, Seattle, Oakland -- led by leaders who are not predisposed to seeing protesters as violent hippies.
