This may affect most KDE installs. Proposing as final blocker per Beta Release criteria: Upgrade requirement "For each one of the release-blocking package sets, it must be possible to successfully complete a direct upgrade from fully updated installations of the last two stable Fedora releases with that package set installed." KDE is a release blocking desktop.

Steps to reproduce:
1. Install F27 KDE Live (final release) image: Fedora-KDE-Live-x86_64-27-1.6.iso in a VM. Use anaconda - Install to Disk.
2. Boot it.
3. Update it: 
  # dnf update --refresh
4. Reboot it.
5. Install the system-upgrade plugin:
  # dnf install python3-dnf-plugin-system-upgrade.noarch
6. Upgrade attempt to F28 reports the same Error:
  # dnf system-upgrade download --releasever=28 --refresh
Before you continue ensure that your system is fully upgraded by running "dnf --refresh upgrade". Do you want to continue [y/N]: y
Fedora 28 - x86_64 - Updates      3.5 kB/s | 257  B     00:00    
Fedora 28 - x86_64                3.6 MB/s |  60 MB     00:16    
Last metadata expiration check: 0:00:00 ago on Tue 03 Apr 2018 11:28:33 PM CEST.
Error: 
 Problem: problem with installed package libkolab-1.0.2-9.fc27.x86_64
  - package libkolab-1.0.2-9.fc27.x86_64 requires libboost_atomic.so.1.64.0()(64bit), but none of the providers can be installed
  - boost-atomic-1.64.0-5.fc27.x86_64 does not belong to a distupgrade repository

It should work with --allowerasing , which may be a sufficient workaround. I suspect this package should just be retired (and properly obsoleted by something): see https://bugzilla.redhat.com/show_bug.cgi?id=1556048 .

libkolabxml-1.1.6-4.fc28 has been submitted as an update to Fedora 28. https://bodhi.fedoraproject.org/updates/FEDORA-2018-1401a88cd6

libkolabxml-1.1.6-4.fc28 has been pushed to the Fedora 28 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2018-1401a88cd6

I upgraded from Fedora 27 KDE and had to remove the following packages before the upgrade would run:

-boost-atomic
-digikam
-libkolab
-mariadb-libs

Unfortunately, I did not take screen shots of messages, but I was similar to what is shown in above posts.

Re-installation of all but mariadb-libs caused no problem. Mariadb-libs is not found by dnf, I suppose it is removed from the packages.

There's no indication in this bug yet about anything about digikam or mariadb-libs (in fact, it would be best to file separate bugs for each)

I'll look into the boost-atomic thing.

I can't tell anything wrong with boost or boost-atomic offhand, but it appears to be related to the libkolab issue highlighted here (ie, if libkolab issue were fixed, boost-atomic would be too)

Yes, this is not a catch-all 'upgrade fail' bug. It is specifically a bug about libkolab. If there are upgrade path issues in other packages, those need to be filed separately.

I can confirm that after adding updates-testing:
  sudo dnf dist-upgrade   --releasever=28  --enablerepo=updates-testing
This error disappeared.

I confirm that the libkolabxml-1.1.6-4.fc28 update fixes the upgrade issue.

Thanks!

Discussed during the 2018-04-09 blocker review meeting: [1]

The decision to classify this bug as a RejectedBlocker and an AcceptedFreezeException was made as it does not violate any existing blocker criteria surrounding default packages, but it is a fairly commonly-installed package, and as such warrants a freeze exception.

[1] https://meetbot.fedoraproject.org/fedora-blocker-review/2018-04-09/f28-blocker-review.2018-04-09-16.01.txt

libkolabxml-1.1.6-4.fc28 has been pushed to the Fedora 28 stable repository. If problems still persist, please make note of it in this bug report.