Oh this is a common issue. You need to sacrifice something to appease the Six Sovereign Sorcerers of SketchUp. Usually just something small like a sandwich or USB stick, but depending on how long since your last sacrifice, you may have to acquire a used furniture item or spare tire.

Seriously though, that's a weird issue. Only thing I can think of is that you could be shift-locking to an inference by accident, in which case hit shift again to unlock.

@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.