Worst performance yet of OnGUI in 2018.2.9 build + script debugging

Hi everyone,

I noticed that my development builds with enabled script debugging are getting an extensive performance hit. A lot more then I'm used to. The Profiler tells me it's primarily bc of OnGUI related unity code (BeginGUI() EndGUI())

I build with .Net 4.x, IL2CPP, C++ Release

I use OnGUI a lot for my debug GUI. An older build I did with 2018.2.6f1 does not show this behavior.

My release builds (stripping out all OnGUI methods) are running at about 60fps , my debug builds formerly did run at about 30fps but now around 3fps.
I didn't change anything related to the GUI nor does anything else show a significant performance drop in the Profiler.

Is this known / does a work around exist?

ps. currently I'm building with 2018.2.15 with the same result.

Edit: to make it clear: as soon as I disable script debugging in the build settings the speeds are up again.