I use a NAS on Linux all the time using NFS and never have a problem. You did not provide enough info to reproduce it since “NAS” is not enough information.
My NAS is Open Media Vault 5 and I don’t use NFS because I have had to many problems with it on some devices. I use Samba (up to date) for file sharing. Like I mentioned, all my other software may it be Gimp, Thunderbird, OpenShot, Audacity, Handbrake you name it, they all work perfectly with my NAS.
Everything with Shotcut works perfectly (save as, open, importing media and exporting too my NAS) but for some odd reason, the save function generates an error, but when using the local drive, It’s fine.
I only gave calibre as a reference, but the problem still exists and the solution is to not use a NAS…
Weird as I use SMB from my Windows and macOS to the machines with no problem either. The code uses the QSaveFile API, which does some things to ensure a more reliable save operation that might be affecting some situations.
It sounds like there is a problem in the setting up of shared folders on your Open Media Vault NAS.
The general usage of QSaveFile is:
Call QSaveFile (this creates a temporary file);
Open the file;
Write to the file;
Call commit();
Commit() renames the file, probably using the Stdio rename function. If the name of the new file is that of an existing file, the function may either fail or overwrite the existing file, depending on the specific system and library implementation… This is probably where your NAS is giving an error.