Stat Panel with variables with expression on several queries display NaN


I want to use a stat panel to display the result of an expression made over 3 different elasticsearch queries. My grafana version : 8.4.6 . In the following elements I simplified my problem with only one query and one expression.

Those queries use a dashboard variable (a map key value)

The query alone with the variable works fine
interval is set to 1 year in order to have only one bucket as result

The query plus the expression A+100 does not display anything. I dont have values for the first query anymore.

They query without the variable plus the expression works fine

Do you guys have an idea of what to do ? Is this a bug , a limitation of grafana or is it me that is not correctly using grafana ?

Thx for the help !