I am running Fedora 31, aarch64 release on many Raspberry PI 3B+.
You don't state which kernel you're running.
I have exactly the same behaviour with all the RPIs.
Are they all 3B+ devices?
When trying to access a NFS server ( perfectly working with my
laptops
running fedora X86) with a ls command when a huge transfer is on going,
I have a lot of "NFS server not responding" in journal and ls is hanged.
I tried to replace the onboard ethernet card with a USB 1GB ethernet and
I don't have this issue at all.
I also tried to change port on the switch with the same result ( not
working with on board card, working with USB one)
I also had such network issue with Fedora 30.
Which kernel are you running with F-30? Are you stating you see the
same issue as on F-31.
Are you aware of such a behavior, if not I will open an issue.
Not had one reported, and there are others using NFS on their
Raspberry Pis. We would need a LOT more information than what you've
supplied, the problem with NFS issues is that they are often very
dependent on the local setup, client/server/switch/network config etc
so are often hard to replicate, especially without a lot of extra
details.