Backups triggered by WP Cron are unreliable

Hi,

Continuing this from my previous posts in the thread called “[Resolved] Total Upkeep Freezes, Says “This Backup Is Taking Longer Than Expected””

Backups triggered by WP Cron are unreliable, but manual backups and Auto Update backups always complete okay.

Since 11th March there have been 12 successful scheduled WP Cron backups, a failure rate of 7/19 = 37%.

An unsuccessful backup results in:
No email notification
A smaller than expected backup zip file
No “More info Show” link on the backup page

I’m using System Zip (compression level 6)
Pre-flight check looks good to me (the only highlight is “System crontab available? No”)

And here’s the log from the latest failed run:

[2021-03-28 16:53:24 UTC] PHP Version: 7.4.15
[2021-03-28 16:53:24 UTC] WordPress Version: 5.7
[2021-03-28 16:53:24 UTC] Total Upkeep version: 1.14.11
[2021-03-28 16:53:24 UTC] Backup process initialized.
[2021-03-28 16:53:25 UTC] --------------------------------------------------------------------------------
[2021-03-28 16:53:25 UTC] Starting dump of database...
[2021-03-28 16:53:25 UTC] Memory usage - limit / current / peak memory usage: 1073741824 / 63366136 (60.43 MB) / 64413120 (61 MB)
[2021-03-28 16:53:26 UTC] Database info: Array
(
    [wp_jettd9_actionscheduler_actions] => 160
    [wp_jettd9_actionscheduler_claims] => 0
    [wp_jettd9_actionscheduler_groups] => 5
    [wp_jettd9_actionscheduler_logs] => 469
    [wp_jettd9_cleantalk_ac_log] => 2709
    [wp_jettd9_cleantalk_sessions] => 100
    [wp_jettd9_cleantalk_sfw] => 9113
    [wp_jettd9_cleantalk_sfw_logs] => 2
    [wp_jettd9_cleantalk_spamscan_logs] => 0
    [wp_jettd9_cleantalk_ua_bl] => 42
    [wp_jettd9_commentmeta] => 0
    [wp_jettd9_comments] => 0
    [wp_jettd9_links] => 0
    [wp_jettd9_options] => 701
    [wp_jettd9_postmeta] => 2173
    [wp_jettd9_posts] => 172
    [wp_jettd9_rank_math_404_logs] => 0
    [wp_jettd9_rank_math_analytics_gsc] => 7257
    [wp_jettd9_rank_math_analytics_objects] => 26
    [wp_jettd9_rank_math_internal_links] => 69
    [wp_jettd9_rank_math_internal_meta] => 30
    [wp_jettd9_rank_math_redirections] => 0
    [wp_jettd9_rank_math_redirections_cache] => 0
    [wp_jettd9_rank_math_sc_analytics] => 2692
    [wp_jettd9_term_relationships] => 78
    [wp_jettd9_term_taxonomy] => 36
    [wp_jettd9_termmeta] => 30
    [wp_jettd9_terms] => 36
    [wp_jettd9_usermeta] => 61
    [wp_jettd9_users] => 1
    [wp_jettd9_wpforms_tasks_meta] => 80
    [wp_jettd9_wpmailsmtp_tasks_meta] => 27
    [wp_jettd9_yoast_indexable] => 247
    [wp_jettd9_yoast_indexable_hierarchy] => 0
    [wp_jettd9_yoast_migrations] => 18
    [wp_jettd9_yoast_primary_term] => 0
    [wp_jettd9_yoast_seo_links] => 112
    [wp_jettd9_yoast_seo_meta] => 110
)

[2021-03-28 16:53:28 UTC] Dump of database complete! $status = 1
[2021-03-28 16:53:28 UTC] Memory usage - limit / current / peak memory usage: 1073741824 / 63437144 (60.50 MB) / 66303808 (63 MB)
[2021-03-28 16:53:28 UTC] --------------------------------------------------------------------------------
[2021-03-28 16:53:47 UTC] Database dump file added to file list: /home/ralph77/boldgrid_backup/soldonhold_com_au.20210328-165326.sql / 9464627 (9.03 MB)
[2021-03-28 16:53:47 UTC] Starting archiving of files. Chosen compressor: php_zip
[2021-03-28 16:53:47 UTC] Memory usage - limit / current / peak memory usage: 1073741824 / 72536872 (69.18 MB) / 73626824 (70 MB)
[2021-03-28 16:53:47 UTC] --------------------------------------------------------------------------------
[2021-03-28 16:53:47 UTC] Starting to analyze filelist...
[2021-03-28 16:53:47 UTC] Memory usage - limit / current / peak memory usage: 1073741824 / 72526616 (69.17 MB) / 74079800 (71 MB)
[2021-03-28 16:53:48 UTC] Finished analyzing filelist!
[2021-03-28 16:53:48 UTC] Memory usage - limit / current / peak memory usage: 1073741824 / 73055216 (69.67 MB) / 74079800 (71 MB)
[2021-03-28 16:55:16 UTC] Total files / size archived: 13515 / 237563300 (226.56 MB)
[2021-03-28 16:55:16 UTC] Starting to close the zip file.
[2021-03-28 16:55:16 UTC] Memory usage - limit / current / peak memory usage: 1073741824 / 73512872 (70.11 MB) / 75063640 (72 MB)