The Flying Geometry SketchUp Bug
Imagine you're in the middle of modeling a project. Suddenly, some geometry snaps to a weird location. You try to undo... No Undo!? 
This bug has been around in SketchUp for years and it seems to mostly happen when autosave catches you in the middle of a tool operation (like when actively clicking with the line tool).
It seems to happen more often with some extensions installed (FlexTools among them), but will also happen without any extensions at all. It depends on how often autosave is set to occur, on how heavy and complex the model is and possibly on how fast you click . . .
Looking for Solutions
We did eventually manage to reproduce the issue, but by that time, the bug was fixed in Sketchup 2021. Hooray!
Solutions
1. The obvious solution is to move to Sketchup 2021!
2. Turn Off Autosave! If moving to Sketchup 2021 is not an option currently, we'd recommend turning off the autosave feature. This will solve the problem immediately!
Go to: Window > Preferences > General > Uncheck 'Auto-save'
3. If you've found autosave useful over the years, maybe you could change it from the default of saving every 5 minutes to something like every 15-30 minutes. This will reduce the chances of the issue happening.
Our Recommendations
Make it a habit to save your models every 10 minutes and at every important stage with a new name, like model_01, model_02, model_03, with a short description.
For quick incremental file naming you can use ComponentFinder. It automatically suggests a name with the next file number when saving- very convenient!
Honestly, when large models are automatically saved every 5 minutes (Sketchup's default) this can waste loads of time, and autosave becomes more harmful than useful. Over the last 10-15 years we used autosaved models maybe only a couple of times.
Every time we install Sketchup we immediately turn off autosave and rely on manual saving - no regrets!
With time 'Save As' becomes a second nature, so . . .
Hope you find this useful!
Special thanks to Arch-Viz Specialist James Steacy from Shoalts & Zaback Architects for inspiring this blog post. 🙂