virtualbox.org

Host: WIn10 / Guest : Win10

The guest will hang if you do nothing to the guest in around 10 minutes.

Host: WIn10 / Guest : Win7

The extra disk (2nd hard disk) in guest will be disappeared after several hours ...

When I change the version back to V6.1.14 , it works normally.

I am new to VBox but I can't say I have seen any issues so far (1week+) with 6.1.16 and CentOS 7 and 8 and Ubuntu 20.04.1. LTS.
I have not done much - just some basic admin work and some containers on CentOS. But I would leave VM running for hours and
have not experienced any issues.

Yes , as you said the 6.1.16 is stable in linux guest ( I am using ubuntu )

I don't know why there are some issues under win7 and win10 guests.

This doesn't sound like a new issue, it sounds like power saving kicking in after 10 minutes, in which case people have been finding this for as long as I've used VirtualBox - it has nothing to do with 6.1.16.

Since a VM doesn't have independant power to save, you should always disable power saving features in the guest OS.

Yes , it's an old issue indeed.
But , I have disabled the power saving function already.
So , the Vbox 6.1.14 works perfectly.
The guest died after I upgrade to V6.1.16.
Switch back to V6.1.14 , perfect again.