Signing in with a link
You can sign in without a password: FlexViz emails you a link instead. For an account made from an invitation, this is the way in until you set a password.
On the login screen, choose Email me a sign-in link instead, enter your address and press Email me a link.
The link works once, for 15 minutes. If it has expired or was already used, the page says so and offers Send me a new link.
The answer on screen is the same whether or not the address has an account, so the form cannot be used to find out who uses FlexViz.
Opening the link shows a Continue to FlexViz button rather than signing you in at once. That is on purpose: mail scanners open every link in a message, and would otherwise use it up before you do.
"I never chose a password"
Colleagues who joined from an invitation without an account only typed their name (see Inviting colleagues). They sign in with a link until they choose to set a password. On their profile, such an account shows Set a Password, without asking for a current one.