What files? Edited with what application? What were you running prior to High Sierra?
Finder tags are tested to work in iCloud, and Apple approved filesystems directly under High Sierra Finder's purview. Apple is not responsible for file attribute information retention (or loss) on Google Drive, Microsoft One Drive, Amazon, or any other non-Apple Cloud service. Especially since they are non-Apple filesystems on the remote side.
If your tag losing file round trip to Google Drive is performed in a browser interface, the file is leaving the Apple filesystem, and there is every opportunity for attribute information to be lost on the Google side. If you are using an APFS SSD, does the installed Google Drive client state that it is compatible with APFS? Is it the most recently available Google Drive client?
In any case, I do not see this as an Apple problem, but one for Google to address.