this is a case of updating a kde shard, which is seems required to pass this problem.
A rationale is:
16.04.3 kde applications has been masked and will be removed from gentoo tree. Those ebuilds still in ports-2012, but tarballs upstream removed as well as downstream on gentoo distfiles.
16.12.3 application releases are stabilized in gentoo but those ebuilds stack are not present in ports-2012 making various troubles such as
1. kde shard update needed by SHA, where 16.12.3 ebuilds stabilized.
2. browse for custom kde fixups applied on top of frozen shard and remove them
3. check whether it require to update any other packages from other shards and apply updates by fixups.
4. run metro kde QA build.