VERR_SSM_LOAD_CONFIG_MISMATCH

[crock]

I know, that this topic has been discussed 12 years ago (ticket/1979). But I still get this error VERR_SSM_LOAD_CONFIG_MISMATCH.
I cannot open the snapshots / VMs with the guest system Windows 7 (I don't know whether it has anything to do with the guest system). All the other VMs with other guest systems are working. I think, the problem only began after I updated to Virtualbox 6.1.12 r139181 and Extension pack 6.1.12 (My host system is Windows 10).
At the end, I had to delete the whole VM (restoring earlier snapshots did not help. They produced the same error). How can this be avoided?

This is the detailed error message I got when trying to open the VM/snapshot:

Failed to open a session for the virtual machine Windows7_64bit_Firefox66.
pci#0: Device vga/0 failed to respond to region #0 size/type changing from 0x0000000004000000/0x8 to 0x0000000004000000/0x0: VERR_SSM_LOAD_CONFIG_MISMATCH [ver=4 pass=final] (VERR_SSM_LOAD_CONFIG_MISMATCH).
Result Code: E_FAIL (0x80004005)
Component: ConsoleWrap
Interface: IConsole {872da645-4a9b-1727-bee2-5585105b9eed}

[mpack]

Caused by upgrading VirtualBox while some VMs were suspended. You need to revert to the previous VirtualBox version of discard the saved state.

Deleting the entire VM was never necessary.