Using top(1) but still get more than one value


I use this line to get the highest value for that month:

SELECT top("value", 1) AS "Users" FROM "metrics" WHERE ("host" = 'ServerName' AND "performanceLabel" = 'Users' AND "time" >= '2018-08-01' AND "time" <= '2018-08-31') AND $timeFilter GROUP BY time(4w) fill(null)

I use this in a Table panel in Grafana but somehow I get more than one value.
I’ve tried to change the 4w to 5,6,7 etc. and the only time I get only one value is when I use 7w, but when I try 8w I get two values again.

Does anyone know why it behaves like this?