No it’s not a networked location.
I just found out that Rhino 6 also crashes when I just open it and do nothing for about 2 minutes. It always crashes after some amount of time, without building or saving anything.
I think the fail to save message is triggered by the crash. Not by the location that it is saved to.
That particular bug was fixed in Rhino 6 a long time ago, so you are most likely running into something else…
Please run the Rhino SystemInfo command and copy-paste the result here.
-wim