That is strange. The link is seen in the log file
https://koji.fedoraproject.org/koji/buildinfo?buildID=1157046 --> x86_64 build.log (https://kojipkgs.fedoraproject.org//packages/grass/7.4.2/1.fc27/data/logs/x86_64/build.log)
"(cd /builddir/build/BUILD/grass-7.4.2/dist.x86_64-redhat-linux-gnu/lib; ln -f -s libgrass_dig220.127.116.11.so /builddir/build/BUILD/grass-7.4.2/dist.x86_64-redhat-linux-gnu/lib/libgrass_dig2.so)"
Checking the package itself:
wget https://kojipkgs.fedoraproject.org//packages/grass/7.4.2/1.fc27/x86_64/grass-libs-7.4.2-1.fc27.x86_64.rpm rpm -qpil grass-libs-7.4.2-1.fc27.x86_64.rpm | grep libgrass_dig /usr/lib64/grass74/lib/libgrass_dig18.104.22.168.so
... the expected symlink is missing. Weird!
As I wrote in the bugzilla issue the upgrade of GRASS will never fix the linked issue. The problem is QGIS, not GRASS: 1) QGIS must be recompiled against any newer version of GRASS and 2) the version available in official Feodra repo is too old (QGIS 2.18.20 is ok, but 2.18.16 is too old).
That's why I'm currently maintaining three COPR repos (qgis, qgis-ltr and qgis-testing) with QGIS for Fedora. I tried some time ago to get in touch with the current maintainer of QGIS with no success, then I'm forced to stay on COPR.