So I have several VMs: Ubuntu Unity 21.04, Trisquel, Pop, Debian 10, Mint 20.1 all of which are up to date in terms of upgrades.
When there is a couple of hours of inactivity, they all display a similar pattern, no internet connection.
However, the relevant control panel shows that the network is connected, more so, while using Terminal (in the guest) I can check the status of the VPN which also informs me that it is connected.
Yet I cannot load a web page. (I have disabled the Kill Switch on the VPN)
They are all connected via Bridged Networking and each VM has an individual IP & MAC addresses so I can see no conflicts here.
It is almost as if there is a time out or switch that flicks off the connection, but doesn't inform the guest OS which mistakenly indicates it is connected.
I had the same problem with Fusion 11 and Catalina.
However, the Windows 10 VM utilising similar settings in it's network adapter does not have this issue. That is to say with the W10 running at the same time as a Linux VM the Windows machine doesn't lose/ drop connection whereas the Linux VM will.