Storyline 360 Versioning on Google Drive for Desktop

Actually, I think it is Windows that is appending the 2 to the file name.

Saving a SL file is a VERY complicated function, and any little anomaly in network latency or transmission can bargle the whole file. Best practice is to download the file from Drive to  local drive, work on it, save locally, then upload to Drive. SL does not allow concurrent usage of the file, so you don’t lose any collaboration, but you do gain reliability.