Since I had a hard time finding an answer online, I decided to make a question here, and answer it myself, so maybe it helps someone:
I have a VirtualBox 6.1 installed on Windows 10, trying to run Centos7.
When I tried to start a VM, I got an error saying something like "Fatal! Could not read from the boot medium".
Then, I powered off the machine, and ticked the checkbox to restore most recent snapshot.
Restoring failed with following error text VERR_SSM_LOAD_CONFIG_MISMATCH :
Failed to open a session for the virtual machine CentOS7 - plus Liferay7- Template.
ahci#0: The target VM is missing a device on port 0.
Please make sure the source and target VMs have compatible storage configurations
[ver=9 pass=final] (VERR_SSM_LOAD_CONFIG_MISMATCH).
Result Code: E_FAIL (0x80004005)
Component: ConsoleWrap
Interface: IConsole {872da645-4a9b-1727-bee2-5585105b9eed}
The core of the problem for me was that virtual storage somehow got detached, so I had to re-attach it manually. Here's what I did:
The VM should now boot normally.
This is how it looked like in the end for me:
Source of my fix: https://www.virtualbox.org/ticket/11750
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