Symptom: you rsync a directory into the local Google Drive for desktop folder (~/Library/CloudStorage/GoogleDrive-<account>/...). rsync reports success. New files appear on other devices. But files that OVERWRITE an existing synced file never upload - they sit on local disk with correct name, size and mtime while every other device shows the stale version. No error anywhere.
Cause: rsync -a without --inplace writes a temp file (.name.XXXXXX) and renames it over the destination. On a FileProvider-backed mount that rename swaps a Drive-tracked item for an untracked one, and the daemon never queues an upload for it. Creation events are handled fine, which is why brand-new filenames always work - it makes the bug look intermittent when it is actually deterministic on overwrite.
Detection: a file that has really reached Google carries the com.google.drivefs.item-id#S extended attribute (Drive writes it only after the server assigns an id). No xattr = local-only, regardless of what rsync said.
xattr -p 'com.google.drivefs.item-id#S' "$MOUNT/path/to/file" # id => uploaded; fails => local-onlyTelling this apart from a genuinely wedged daemon (which looks identical): write a sentinel directly to the mount and see if it gets an id within ~15s. Healthy daemon + stuck file = the rsync overwrite bug.
Fix for a stuck file: delete the mount copy and plain-cp it back, which produces a creation event (uploaded in ~25s in my case). Prevention: use rsync --inplace for FileProvider destinations, or copy instead of rsync.
Two related traps: (1) a live process and a freshly-written log prove nothing about upload health - I had a 51 MB file unsent for 20 hours while the daemon logged every minute; (2) never run an unbounded find/stat/xattr over the mount - a wedged or re-indexing FileProvider blocks forever on paths it has not materialized, so a find $MOUNT -type f hangs rather than fails. Enumerate from the real local disk and check specific relative paths with a per-call timeout.
Versions: Google Drive for desktop 129.0.1.0, macOS 25.5 (Darwin).