Job backup failed for first time: "!!!Error: Update job history failed"

I've been using the same backup schedule now for a year: A full backup every 5 weeks with weekly incremental backups in between.

For the first time, HDM 16 reported that the full backup failed last night.

Even though jobs_db.log shows that a full backup of all files was created on the backup drive,

the jobs.log file shows this:

[12740]: (Retention) Scan storage directory for archives : 'F:/Paragon Backups/Job-201881215632'
[12740]: (Retention) Number of backup sets for retention : 3
[12740]: (Retention) Number of archives for retention : 11
[12740]: (Retention) Oldest backup set found for retention : 'F:/Paragon Backups/Job-201881215632/Job-201881215632_2018-12-22_00-05-12'
[12740]: (Retention) Number of archives in set for retention : 5
[12740]: (Retention) Number of archives need for retention : 15
[12740]: (Retention) Number of archives is not enough for retention ... Stop

[12740]: !!!Error: Update job 'dcd5b133-e2b6-4d5f-b650-30c7403b6417' history ... Failed (Result = 0x11047, "F:\BuildAgent\work\cd106b9f4c54ea60\hdmengine\hdm sdk\src\stub1\job\job_stub1.cpp, $Revision: 287693 $, line 993")

[12740]: !!!Error: Perform job 'dcd5b133-e2b6-4d5f-b650-30c7403b6417' ... Failed (Result = 0x11047, "F:\BuildAgent\work\cd106b9f4c54ea60\hdmengine\hdm sdk\src\stub1\job\job_stub1.cpp, $Revision: 287693 $, line 1018")

[12740]: JOB_Job_Do result: 0x11047 (!!!Error: "The selected path is not available, please check and retry.")
[12740]: Finish time: 02.03.2019 02:15:10

That path makes no sense, because F: is the backup drive and there is no top-level folder called BuildAgent in it. No previous backup ever complained about this. All the backup jobs have been going correctly to the folder F:\Paragon Backups up till now.