Have a Sketchup model where one user opens it and changes material settings and saves. Second user opens it on another machine and edited materials revert to previous state. Identical specs on both machines.
The material settings themselves are actually changing (i.e. RGB values saved as 91/91/91 are changing to 191/191/191, materials that had textures removed still have them when reopened).
Opened the same file on two different machines simultaneously and materials had different settings in each instance.
Tested on multiple other machines with the same file (opened as read only multiple times), and sometimes materials showed edited versions and sometimes showed previous versions.