Does the CUCM version in CER say "14" or "14.0"?  I've run into a bug where the version was set to 14 and had to be changed using the GUI to 14.0.  Your log should also reflect that slight difference.

How did you upgrade the phones? That version of firmware for those phones was the base firmware of an older devicepack (https://www.cisco.com/web/software/282074299/124017/cmterm-devicepack10.5.2_12014-1_Release_Notes.pdf)I suggest following the ins...