What does that mean: packages excluded due to repository priority protections

Solution 1:

From what I understand, this error is generated from the priorities plugin as noted by Pawel.

In 2009, the maintainer of yum mentioned that he hoped people would not use priorities. To disable the priorities plugin, edit /etc/yum/pluginconf.d/priorities.conf and set enabled = 0. After this change, next time you run yum update, you should not get any priority protections.

Solution 2:

Some packages are held by more than one repository. The priorities plugin choose packages from the highest-priority repository, excluding duplicate entries from other repos.

Solution 3:

In case you want to know which packages are excluded due to priority protections you can use

yum list updates -d3