"There were errors while loading the file."

[zigpot]

I opened the FreeCAD_DEMO_grindplate.FCStd file and a warning appears on the bottom:

There were errors while loading the file. Some data might have been modified or not recovered at all, Look above for more specific information about the objects

it also seems that selecting file in Combo View > Model doesn't show information and also the features are Unnamed:

OS: Ubuntu 20.04.3 LTS
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.4.
Build type: Release
Python version: 3.8.2
Qt version: 5.12.5
Coin version: 4.0.0
OCC version: 7.3.0
Locale: English/United States (en_US)