One Comment on our internal Chat board said:

• Got "Reason: Unknown error. Check the configuration for the identity source and identity router, then resynchronize" instead of "Update user information failed. Reason: Unspecified"
• Expected user to be disabled. But was enabled

Another comment said:

tc003_disabledUsers_should_be_excluded_during_MFAUserLookup.01 -STACKTRACE

java.lang.AssertionError: The following asserts failed:

Verify [×

Update user information failed. Reason: Unknown error. Check the configuration for the identity source and identity router, then resynchronize.] contains [Update user information failed. Reason: Unspecified.]: expected [true] but found [false]

So maybe check user status in Identity Source and in any Challenge User group lookup