x11-apps/copyq has some dependencies like dev-qt/qtcore:5=, but dev-qt/* currently does not explicitly define subslots so the behaviour is undefined. In the future, dev-qt/* will define a subslot, but that will only be required for a very limited number of packages. I can't see any use of private API or relevant compile-time conditionals, so please remove the subslot operators to avoid triggered unnecessary rebuilds.
https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=1ca760da3c7b6934f44758f0f011746802bc20f2