Something seems to have gone wrong with the maximum polygon count (or something similar) after the latest 12-19-2018 update. Complicated designs that previously worked fine are now permanently stuck in the red "Node Failed to Load" zone.
This has affected a couple of my designs as well as the designs of some of my friends.
I don't know if there's anything that can be done to fix this. Unfortunately, the download feature is also broken, and clicking Unmerge (which used to work for me in the past if I crossed that virtual threshold into unhappy node land) flounders and fails because it can't load the shapes to begin with.
TinkerCAD really needs a "safe mode" that will let you load a shape as a solid object without it's entire back history if it gets a node failure.
Here's an example link of one of the designs being affected: https://www.tinkercad.com/things/67trUQCntJS-8th-doctor-tardis-console (this one was previously published as public so anyone can access it, but it can no longer be edited or downloaded)
Anyone got any suggestions? TinkerCAD is the most amazing free CAD program I've ever used, so I can't knock it too much when this happens, but it's especially frustrating when a design fails retroactively, so there's no way to go back to a previous safe state.