Hello, the synchronization of that repo is failing also for succeeded builds. See, e.g. here:
https://copr-be.cloud.fedoraproject.org/results/chambridge/qpc/fedora-27-x86_64/00705366-qpc/builder-live.log
That means that doesn't cause the problem. You can find the message:

Failed to synchronize cache for repo 'http_download_fedoraproject_org_pub_epel_releasever_basearch', disabling.

I can see two problems actually, one for f27 and the second for 26. For f27:

https://copr-be.cloud.fedoraproject.org/results/chambridge/qpc/fedora-27-x86_64/00705084-qpc/builder-live.log

See the message here:

https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/message/HNFA7Y32SMHUB7XZ3RGDP4IAJ4ZUPXR4/

And for f26 builds, e.g. here:

https://copr-be.cloud.fedoraproject.org/results/chambridge/qpc/fedora-26-ppc64le/00705346-qpc/builder-live.log

those are unsatisifed deps:

Error:
Problem: package pkgconf-1.3.7-1.fc26.ppc64le requires libpkgconf(ppc-64) = 1.3.7-1.fc26, but none of the providers can be installed
- cannot install both libpkgconf-1.3.12-2.fc26.ppc64le and libpkgconf-1.3.7-1.fc26.ppc64le
- cannot install the best update candidate for package pkgconf-1.3.7-1.fc26.ppc64le
- cannot install the best update candidate for package libpkgconf-1.3.7-1.fc26.ppc64le

So I recommend exploring those.