Many users have complained about degraded performance on their consoles after installing the latest PS4 System Software Update 9.00. While many consoles are unaffected, a few have been rendered unusable. Sony is yet to issue a statement on the matter.
https://www.notebookcheck.net/PS4-System-Software-Update-9-00-reportedly-causing-performance-issues-in-some-consoles.562355.0.html
I have yet to update either of my PS4s. Gonna wait this one out. Given their update history, there should be another update in 2-4 months from the time I post this comment.