Trivial thoughts from reading this thread. Please don't take the
triviality as an insult.
Perhaps the best way to determine if the problem is from a software update
is to downgrade likely packages. In the case of the kernel, you can just
boot an older one (assuming that an old enough one is still installed --
fedora sure has a lot of package churn).
In case the HDDs are the problem, consider running S.M.A.R.T. drive
self-tests on them. I know you said that smartctl reports no errors but
you didn't say whether you've run the drive self-tests.
Is the pause long enough for you to figure out what is hanging? On either
side? (I haven't used NFS for a couple of decades so I'm pretty rusty on
the tooling.)