Thanks for the stats, which were overlooked when you listed them earlier. Clips in the well organized bin folders should not move or change.
You say that you are running 10.47. That likely was a 32-bit version that ran out of memory.
Install this 64-bit release, which is more capable for sizable projects.
No crashes here, but it appears that the effort isn't quite complete - with some video and audio holes.
For export, lower resolution to 1920x1080 at the highest, or perhaps 1024x576 Wide or 1280x720. This will shorten export time. No need for Ultra High Def 3840x2160. What's shown in the box is but a suggestion, based on the resolution of some content.
Again, it's not clear how you 'grouped' but there should be no issue placing clips on the timeline though that can affect the placement of other clips in certain circumstances.
Carry on with the version linked above and be sure to SAVE AS routinely.
Let us know.