Verify disk reports error, recovery os repair + fsck says disk is fine

After my time machine backups got stuck to finish at some point, I decided to do a disk check using disk util.

I'm getting the following output while running "verify disk":

The volume 86A26AC7-8D39-4917-AF77-2F25314852EA appears to be OK Storage system check exit code is 0. Verifying file system. Using live mode. Performing live verification. Checking Journaled HFS Plus volume. Checking catalog hierarchy. (It should be 28985392 instead of 28450688) File system check exit code is 8. Error: This disk needs to be repaired using the Recovery HD. Restart your computer, holding down the Command key and the R key until you see the Apple logo. When the OS X Utilities window appears, choose Disk Utility.

Unfortunately restarting into recovery mode and running "repair disk" doesn't find any errors at all. I've even booted into single user mode for running fsck also without any results - disk was reported as OK. It seems that the FS error only happens after regular booting up.

Disk is a SSD in MBP on Yosemite. Seems to work fine beside this error and stuck backups.

Any ideas to to fix this FS issue?