Chart is always error after refreshing the page

Has anyone encountered this kind of error in Looker?

When I use a SWITCH CASE statement in a calculation and then refresh the page, the chart displays the error: “Looker Studio has encountered a system error.” It keeps annoying me, and the metric name always changes to the default name “New Field” instead of using the name I originally assigned.

switch case statement:

CASE WHEN SUM(Target Sales) = 0 THEN SUM(TotalSales)
ELSE SUM(COALESCE(TotalSales,0)) - SUM((Target Sales)) END