I think there's an issue with the delta bar. Sometimes, it counts invalid laps as a valid one, and after that the delta is still based on the real fastest (and valid) lap, but the delta bar shows the wrong session fastest lap and the predicted gets wrong too.

It could he difficult to reproduce the bug, as it doesn't always happen.

As you can see on the screenshot, my real fastest lap is the one you can see in standings, and the unvalid one is the best session lap on the delta bar.