I went back six hours. Here is the report from Terminal (substituting "[user]" for my name):
Last login: Mon Jan 15 15:38:05 on ttys000
Macintosh:~ [user]$ log show --predicate 'subsystem == "com.apple.TimeMachine"' --info --last 6h | grep -F 'eMac' | grep -Fv 'etat' | awk -F']' '{print substr($0,1,19), $NF}'
2018-01-15 10:01:57 Starting automatic backup
2018-01-15 10:02:05 Backing up to /dev/disk2s2: /Volumes/Time Machine Backups/Backups.backupdb
2018-01-15 10:02:15 Event store UUIDs don't match for volume: 499GB HD
2018-01-15 10:03:10 Deep event scan at path:/ reason:must scan subdirs|new event db|
2018-01-15 10:03:10 Reading cached event database from: /Volumes/Time Machine Backups/Backups.backupdb/Mac mini/2018-01-15-100215.inProgress/2A236B97-F5B5-4B11-808A-8C5A387F7532/.06E5C76 9-B2DE-3624-8388-0AB0182B4D63.eventdb
2018-01-15 10:03:10 Unable to use cached scan; fsevent uuid mismatch (5EA06588-87AD-476A-87DA-597D17F3EFC4 vs 1B3FFCC2-5201-4EBA-91EC-252F1DA6E037)
2018-01-15 10:03:10 Running event scan
2018-01-15 11:10:53 Finished scan
2018-01-15 11:10:54 Saved event cache at /Volumes/Time Machine Backups/Backups.backupdb/Mac mini/2018-01-15-100215.inProgress/204A093A-CAD7-4865-9774-5C6883F0C403/.06E5C76 9-B2DE-3624-8388-0AB0182B4D63.eventdb
2018-01-15 11:10:54 Not using file event preflight for /
2018-01-15 12:11:58 Will copy (Zero KB) from 499GB HD
2018-01-15 12:12:05 Backup canceled.
2018-01-15 12:14:24 Not starting scheduled Time Machine backup: Automatic backups disabled
2018-01-15 12:18:27 Starting manual backup
2018-01-15 12:18:36 Backing up to /dev/disk2s2: /Volumes/Time Machine Backups/Backups.backupdb
2018-01-15 12:18:49 Event store UUIDs don't match for volume: 499GB HD
2018-01-15 12:18:49 Waiting for index to be ready (100)
2018-01-15 12:18:56 com.apple.TMHelperAgent.SetupOffer enabled
2018-01-15 12:19:03 Backup canceled.
2018-01-15 12:19:18 Starting manual backup
2018-01-15 12:19:18 Backing up to /dev/disk2s2: /Volumes/Time Machine Backups/Backups.backupdb
2018-01-15 12:19:41 Event store UUIDs don't match for volume: 499GB HD
2018-01-15 12:19:42 Waiting for index to be ready (100)
2018-01-15 12:20:05 Deep event scan at path:/ reason:must scan subdirs|new event db|
2018-01-15 12:20:05 Reading cached event database from: /Volumes/Time Machine Backups/Backups.backupdb/Mac mini/2018-01-15-121941.inProgress/204A093A-CAD7-4865-9774-5C6883F0C403/.06E5C76 9-B2DE-3624-8388-0AB0182B4D63.eventdb
2018-01-15 12:20:05 Using cached disk scan
2018-01-15 12:20:05 Saved event cache at /Volumes/Time Machine Backups/Backups.backupdb/Mac mini/2018-01-15-121941.inProgress/A0801B9E-D839-40E9-8847-2A55A78400E3/.06E5C76 9-B2DE-3624-8388-0AB0182B4D63.eventdb
2018-01-15 12:20:05 Not using file event preflight for /
2018-01-15 12:48:49 com.apple.TMHelperAgent.SetupOffer enabled
2018-01-15 12:48:49 Will copy (Zero KB) from 499GB HD
2018-01-15 12:49:01 Backup canceled.
2018-01-15 13:15:00 Not starting scheduled Time Machine backup: Automatic backups disabled
2018-01-15 14:05:25 com.apple.TMHelperAgent.SetupOffer enabled
2018-01-15 14:07:34 Starting manual backup
2018-01-15 14:07:35 Backing up to /dev/disk2s2: /Volumes/Time Machine Backups/Backups.backupdb
2018-01-15 14:07:54 Event store UUIDs don't match for volume: 499GB HD
2018-01-15 14:07:54 Waiting for index to be ready (100)
2018-01-15 14:08:20 Deep event scan at path:/ reason:must scan subdirs|new event db|
2018-01-15 14:08:20 Reading cached event database from: /Volumes/Time Machine Backups/Backups.backupdb/Mac mini/2018-01-15-140753.inProgress/204A093A-CAD7-4865-9774-5C6883F0C403/.06E5C76 9-B2DE-3624-8388-0AB0182B4D63.eventdb
2018-01-15 14:08:20 Using cached disk scan
2018-01-15 14:08:20 Saved event cache at /Volumes/Time Machine Backups/Backups.backupdb/Mac mini/2018-01-15-140753.inProgress/383893AD-59C0-43F0-81DE-29AB1A27C306/.06E5C76 9-B2DE-3624-8388-0AB0182B4D63.eventdb
2018-01-15 14:08:20 Not using file event preflight for /
2018-01-15 14:23:02 Not starting scheduled Time Machine backup: Backup already running
2018-01-15 15:18:53 Not starting scheduled Time Machine backup: Backup already running
Macintosh:~ [user]$
Macintosh:~ [user]$
Macintosh:~ [user]$