Just for clarity, what you currently see in rFactor 2 is not my plugin, but a version of delta that S397 worked on to integrate it into the standard HUD. Plugins that draw to the screen with DirectX APIs like Delta Best was, can not work anymore, until S397 publishes a new HTML-based API (and they haven't done that yet, and I don't know when that will happen).
For me its the same with the s397 hud, but with red 9999999. It takes 4-5 laps to get proper delta times.
As explained elsewhere, only the first timed lap gets stuck. As long as you do a faster second lap, it works fine.