I recently expanded the capacity of my Google Drive by opting for the 1 TB option. This lead me to embark upon uploading my music collection. To set the scene I am using an iMac and I am connected to the internet via CableOne's business service with a 50 Mbs download capacity and, a modest, 3 Mbs upload capacity. For the purposes of this blog, I'm pretty sure the Mac part is irrelevant.
I was plagued by frequent 'unable to connect' message every few minutes, which would put the sync on hold until some retry interval had it recommence for a few minutes, and then the same cycle would repeat.
The clue to the solution could be found in the affect I was having on the rest of the household. I was swamping the upload capacity of my internet connection. For example, no browsers on the network could get to web pages etc. Well that was hardly surprising, many people don't know that the upload speed of their home internet connection is so modest. "I have a 100 Mbs Internet connection" - well go read the small print, that's just your download speed. Anyway - like I said - no surprise. However, the secret is, that as well as the sync data moving up or down your connection to Google, there is also management information in regard to what needs syncing/deleting/renaming, and also a heartbeat signal to verify connectivity. When you swamp your upload link, this information cannot get through - just like the other members of the household cannot get to the web. So the heartbeat fails and the client tears-down the connection with an error.
If you look at the advanced tab in the Google Drive preferences, you will see a control to throttle the upload/download speeds. You want to reduce that to a little under your upload bandwidth. You can also experiment a little. Bottom line, it will be a slightly slower sync, but overall the jobs are going to run much faster, this they will run continuously and without error.
Cheers and Happy New Year!