The value shown as Min (in the same line as Output Pixel Clock ) is the correct value. I.e, 84.42MHz in your case.
This is a bug in the MIPI configuration tool and we will be fixing it in the next revision of the tool. You may ignore the error as the Output pixel clock value configured (99.9MHz in your case) is in between the Min and Max values.
It is better to keep the Pre-divider value as 3 and adjust the Multiplier of Unit Clock to change the Output pixel clock.
Thank you for your response and recommendation.
I'll ignore this error and try to tune by using pre-divider=3.