I was doing an audit of flight data, and saw that I was seeing flights from an unknown-to-my-system PP-VTR; not sure where in the chain of data the error is coming from, but, it looks like PP-VTR became TF-ISR (an Icelandair B752) in 2016; it looks like it was correctly ID’d in your system until fairly recently, when it started showing up at PP-VTR.
In summary: PP-VTR doesn’t exist; should be showing as TF-ISR.