Adding custom column with If function

is the [Recence] field a string? if so, it should say 

if Number.From([Recence]) < 30, etc.

You cannot compare numbers to text. You will get errors. I suspect it is because before you were getting no errors, so [Recence] must be text as well.

Additionally, if [Recence] should be a number all the way round, just convert the field to a number. In the upper left of the column it probalby has ABC for text. Click on that and convert it to either a decimal number or whole number. Then you don't have to use Number.From() around it. Do that very early in your Power Query steps, before adding any custom columns.