File access lost after some minutes

[Tom Test]

Hello,
I've created a VeraCrypt container file and saved it on a shared network volume.
By mounting the container I have access to all folders and files.
After some minutes I can still see all folders and files but if I try to open a file I've lost obviously the access rights.
I checked the preferences and can not find any settings to avoid this behavior.
Also I've tried this with two different laptops with the same result.

Any ideas???

Thanks...