Fedora Copr builders were recently upgraded to Fedora 30 (from F28).
The major change is that `yum` package is not working ideally on F30
anymore, and soon (on F31) there will be no `yum` at all .
Mock (which is used on builders) though uses /usr/bin/yum-deprecated (yum)
by default for epel* chroots installation usually (on Fedora host), even
though it may use /usr/bin/yum symlink to /usr/bin/dnf as a fallback.
The major difference from mock perspective (and why yum-deprecated is
actually preferred, when available) is that dnf might calculate the
install transactions a little bit differently from yum. And repositories
for epel are designed for/tested against yum; ... so using dnf can cause
some unexpected problems..
We decided to move to dnf (dnf-yum) rather sooner in Copr, to have a bit
more time for solving potential problems, and inform others. So if you
face any related issues to this movement in copr (packages were installed
fine before, but are not now), you might want to enable the
bootstrap_chroot feature in your copr project; go to:
Project -> Settings
-> [x] Enable mock's use_bootstrap_container experimental feature
.. and if useful, fill a bug report. For more info about bootstrap_chroot
feature consult the man 1 mock.
As a bonus, we now have builders (F30) for aarch64 architecture! Expect
slightly slower queue processing there than on other architectures (only
up 8 builders, and slightly slower boxes). Feel free to try them, and - as
always - please report the issues :-)
If you happen to work with epel* and mock on F30:
- yum.rpm requires up2date urlgrabber package (rhbz#1707657) on highly
python3-oriented F30, and to avoid unnecessary hassle you might want
to rather uninstall yum package, but when you do this..
- using dnf (/bin/yum) for epel* builds might lead to problems with
bootstrap chroot installation (elfutils from DTS from sclo* repos
installed instead of default elfutils) 
- also systemd-resolved running on host (even when it is unused) might
cause some problems with name resolution in --bootstrap chroot, resp.
if you happen to use --enable-network; work-around is to disable
Hope that the transition will be smooth, happy building!