What I did and what happened:
- started a new trial
- created a couple of accounts
- enable "Require any MFA" policy for all the accounts
At this point I wanted to enable MY OWN mfa... but I wasn't able to find a place to do it (at least not in the Admin interface, where I was working – right?)
So I logged out of the account and... at the next login LastPass wasn't able to recognise my master password (which was 100% correct).
I had for this reason to reset my account (luckily it was still empty) so that I could finally enter again (using the same master password, of course).
Great job, LastPass.
Advice: the first thing you should do with Enterprise is to create another Super Admin account (they can reset the master password)