This has been explained well by @anon44418554 in this post:
Changing your master password cannot corrupt your vault. The vault can only become corrupted if you first rotate your “account encryption key” (a.k.a. Generated Symmetric Key) in the web app while other client apps remain logged in (using a now “stale” account encryption key), and if you subsequently attempt to use one of client apps to update the vault.
This has implications for those who use disk imaging software to back up their systems – if you rotate your encryption key and subsequently have to restore a disk image that contains locked vaults from before the key rotation, you will corrupt your web vault if you open a client app and make modifications to vault items.