Do you have client logs for 144074443, 144075243, and 144073987 as they re-uploaded their bookmarks to the spanner node, which they should not have done?
Bug 1631787 Comment 17 Edit History
Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.
I think we have determined the sync problems/data loss with node sync-815-us-west-2 are because of the workflow. Neither the client nor the server had the data, so there was nothing to sync. Do you have client logs for 144074443, 144075243, and 144073987 as they re-uploaded their bookmarks to the spanner node, which they should not have done?