CAUSE: There are two LUA accounts with the same cell phone number. This could happen in two scenarios: 1) A user initially logs in with one email address, but then later attempts to log in with a different one, commonly due to a name change. 2) A former employee's Lua account contains the same cell phone number that is now in the new employee's ADUC account.
SOLUTION: Lua Admin / IT-- There are different solutions based on the scenario. For scenario #1, send a Lua message to the "Lua SSO Issue" group and ask for the email address to be updated in the Lua backend database. For scenario #2, find the account with the duplicate cell phone number in the Lua Admin console and remove the cell phone number from it. If it is a former employee, also disable that account.