Time Machine on Time Capsule backup verification never seems to complete
Since the verification process is akin to running fsck the filesystem check utility, this is the thing that will repair the backup or pronounce it dead.

If it fails too many times, you will then be left with a read-only Time Machine directory that you could clone somewhere else, restore the files you care, or wipe and start over.

Sadly, you are seeing all the progress that is normally available without running the tmdiagnose tool to collect detailed status and log when you ask Apple or a technician to help with time machine problems.

In most cases, I would say pick a time you can afford to be without backups (a day, a long weekend, a week) and set the Mac to not sleep and let it chug and see if it finishes. At the end of the period, you can decide to clone off the data to an attached USB drive just in case you need to retrieve something or just wipe the disk and start over.

Have you rebooted your Mac and run a filesystem check (or safe boot) to make sure your Mac doesn't have any directory damage?