Okay, here's a new model. I was having issues with it yesterday that caused me to finally reach out and bother you. I spent the last couple of hours working with no issues, but finally ran into some. Like I said, this does not seem to be specific to any model, nor is is consistent within any model. I was finally able to replicate the issue and noticed that it does seem to happen when I am trying to move copy a single line from an edge within a face. I'm not sure now that you will be able to see anything as it took me a couple of hours to recreate, whitecoat syndrome I guess... I use alt because it is the same as the option key on my computer. As-Builts.skp

@marrigoround said: Are there any performance benchmarks or file sizes that could ease my concerns? Well, it's always wise to keep your file size at a minimum. Also reduce the number of entities displayed in the SketchUp file by assigning layers and turning off visibility of layers for things that aren't shown. For example, in your scenes of the bars from your model, there's really no need for the 2d people and the assembled cart to be shown. Assign layers to them and turn off those layers for the scenes. This helps to reduce the edges LO needs to iterate through when rendering. There are other things you can do to prevent file size bloat in SketchUp that are worthwhile too. On the bright side, LO2016 is lightning fast with rendering compared with LO3 and earlier.