Hi, I am a developer at BuildEdge.
I investigated this problem. Here are my findings.
The simple act of adding a Sketchup::EntitiesObserver to the model seems to trigger a crash in 2DTools (at least in 2D Fillet, which is the only one I looked at). Please see the attached TriggerCrashIn2DTools.rb file. You can disable BuildEdge plugin and activate this plugin. You should still observe the crash.
I think this is a Sketchup bug, but that being said I also found a workaround for 2DTools so that it doesn't trigger this crash. I am attaching a patch for 2DfilletTool.rb. The trick is to delay the erasing of original group after the first model.commit_operation. See the attached patch for details (patch.diff.txt).
A plugin that will cause 2DTools to crash.