Going on past experience, if I have done a "dnf update", then did
another one within a certain time period no attempt was made to see if
data needed refreshing. That time period could be longer than you'd
expect it.
I've been in the situation where running a dnf check-upgrade has
refreshed the two Fedora Updates repositories and then issued dnf
upgrade immediately after and had it refresh the two updates
repositories again. I've been told from this mail list that for the
Updates repositories that is normal as they are being updated all
the time.