I suggest using strace to find out where the delay is happening. I found a
bug
where wonky mirrors were responsible for the hang, and made some
adjustments to dnf to make it decidedly less tolerant of such mirrors.
https://bugzilla.redhat.com/show_bug.cgi?id=1294953
The more recent one bugging me is downloading those metadata files 2-3
times per day even after clean all (once right after is expected, but again
4 hours later no.)
Chris Murphy