I just bought a new MacBook Air running OS 10.14.3 (Mojave). I copied the hard disk from my old MacBook Air over to this new one. Now, when I try to run a Time Machine backup on my WD My Passport Ultra, it won’t work. When I click “backup now,” it acts like a backup is underway, but there is no evidence of a backup in the backups.backupdb folder on the external hard drive when it’s done. There is only a file with today’s date and “inprogress” at the end of its name. I’ve tried removing this “inprogress” file and restarting but that doesn’t fix it. Anybody else having this problem? Is there a solution?
Did you check after re-configuring the Time Machine, manually create the backup on My Passport Ultra?
If not, then follow instructions from the below article to manually create a Time Machine backup.