Sony released a new firmware update for all PS4 users yesterday, but it looks like there's a glitch that's hitting many of those who installed it, at least that's what people think is happening.
Firmware 4.72, according to multiple reports on Reddit, seems to show certain players offline despite them actually being online.
This looks more like a visual glitch than anything else, since most of those affected report being able to see their online friends, what they're playing, and the currently active parties. What looks to be happening is that the console is forcing users into the 'appear offline' state.
For other players, the problem is more than simply seeing a red X next to their name, as it's interfering with their ability to play online and invite others. It's not clear exactly what's causing this, whether it's the new firmware or a general PSN problem that coincidentally happened hours after the firmware launched.
Sony's server status site doesn't mention any ongoing issues, and the official Ask PlayStation Twitter didn't announce any widespread problems when some of those affected got in touch. Seeing that you need 4.72 installed in order to get online in the first place, it may be tricky for those outside Sony to pinpoint the root cause.
Restarting the PS4, and power cycling the router are among the solutions thrown around, but there's no guarantee if any of them will work. Right now, depending on how the game you're playing handles offline mode, you may lose access to certain features even though you're online until the issue is fixed.