Decipher diskutil error code Checking catalog hierarchy
The volume   could not be verified completely
Volume repair complete
Updating boot support partitions for the volume as required
Error: -69845: File system verify or repair failed
Underlying error: 8: POSIX reports: Exec format error


Initial searches on the Apple discussion sites show both the 69845 error coming up, and the posix line too, but so far no joy in either understanding or fixing these two errors.
I've been doing computer support professionally for a number of years (Macs and PCs) and have found one thing to be true: It matters less what the error is than if you can fix it. Hence reinstalling OS, Apps and the like are often the solution rather than hunting down the subtle error.

With that in mind what Disk Utility is telling you is, "I can't fix that." And in situations like that it is time to turn to third party disk utilities. I've been using Disk Warrior since the OS9 days (possibly earlier...) and have found few issues it will not fix. That is how I would proceed. If you have other third party disk utilities (Drive Genius, TechTool pro, etc.) by all means use one of those. But if you have none I would start with DiskWarrior (I have no interest in the company just a happy customer).

Once you have fixed the issue you'll have plenty of time to research the cause of those specific error codes.