Here it is part of the error log:
12-07-2019 04:14:31.1562904871.2278 [116.203.184.52][5d2809][info] Start cron job. Scope: media-library
12-07-2019 04:14:32.1562904872.1018 [116.203.184.52][5d2809][error] Failed to find original attachment #68440 located in *empty path*. Skipping optimization. This may be caused due to bug in wp_get_attachment_metadata() function, which returns false for attachment meta
12-07-2019 04:14:32.1562904872.105 [116.203.184.52][5d2809][error] Failed to find original attachment #68441 located in *empty path*. Skipping optimization. This may be caused due to bug in wp_get_attachment_metadata() function, which returns false for attachment meta
12-07-2019 04:14:32.1562904872.1084 [116.203.184.52][5d2809][error] Failed to find original attachment #68443 located in *empty path*. Skipping optimization. This may be caused due to bug in wp_get_attachment_metadata() function, which returns false for attachment meta
12-07-2019 04:14:32.1562904872.1138 [116.203.184.52][5d2809][error] Failed to find original attachment #68444 located in *empty path*. Skipping optimization. This may be caused due to bug in wp_get_attachment_metadata() function, which returns false for attachment meta
12-07-2019 04:14:32.1562904872.1185 [116.203.184.52][5d2809][error] Failed to find original attachment #68445 located in *empty path*. Skipping optimization. This may be caused due to bug in wp_get_attachment_metadata() function, which returns false for attachment meta