Here's my problem, when I create a part and save it to a network disk it's ok. When this part is created and I want to save any change, Solidworks gives me an error (the backup failed).
Digging a little deeper I noticed that SW couldn't find the part on the network disk while it is beautiful and present. SW actually loses the reference of the part I'm working on...
ok so for me it's a momentary loss of the network.
When the file is opened from the network you have a Windows marker which is created in the same place as the file, if there is a micro-cut in the network it must lose a little of these small ones.
So when you re-save on the network by overwriting the file it regenerates the opening windows marker and it works, locally it works too (normal to save as since you don't save in the same place as the file you initially opened).
It's up to you to see with the IT department to analyze what is happening on the network connection.
This is equivalent, but a network drive not used for X amount of time is disconnected (a problem specific to windows), while a UNC path still remains active (unless there are micro-breaks as indicated by Franck)
The save as window necessarily appears because not finding the path it is waiting for you to indicate a new path or new name (in case the document locks).
It is normal for an error to appear when clicking save directly. If Windows has lost the connection of the network drive, you have to reactivate this connection, for this you have to make it, in a way, read a part so that windows recovers preview and info (property of the part). This operation sometimes freezes windows for a more or less long time, it will depend on the quality of your network...