Following is the log from one complete backup cycle which has only a single dropped fsevent couplet and might be helpful:
17-11-18 1:19:16.235 com.apple.backupd: Starting standard backup
17-11-18 1:19:16.602 com.apple.backupd: Backing up to: /Volumes/Mac Backup/Backups.backupdb
17-11-18 1:19:40.252 com.apple.backupd: 4.52 GB required (including padding), 679.47 GB available
17-11-18 1:19:58.000 kernel: add_fsevent: unable to get path for vp 0xffffff800b50fc98 (app.com.apple.DiskUtility.playlist; ret 22; type 9)
17-11-18 1:19:58.000 kernel: add_fsevent: unabled to get a path for vp 0xffffff800b50fc98. dropping the event.
17-11-18 1:20:00.623 com.apple.backupd: Copied 1148 files (16.9 MB) from volume Mac.
17-11-18 1:20:00.768 com.apple.backupd: 4.50 GB required (including padding), 679.45 GB available
17-11-18 1:20:04.614 com.apple.backupd: Copied 670 files (433 bytes) from volume Mac.
17-11-18 1:20:06.409 mds: (Error) Volume: Could not find requested backup type:2 for volume
17-11-18 1:20:06.412 com.apple.backupd: Starting post-backup thinning
17-11-18 1:20:24.280 com.apple.backupd: Deleted /Volumes/Mac Backup/Backups.backupdb/grelber’s iMac/2017-11-16-181500 (17.7 MB)
17-11-18 1:20:24.280 com.apple.backupd: Post-back up thinning complete: 1 expired backups removed
17-11-18 1:20:24.716 com.apple.backupd: Backup completed successfully.
[Note: The mds error (line 9) occurs in every backup but seems to have no significance.]
