What is the effect of the data source on a table visual loading?

Hi amitchandak, yes it seems to be the measure that is causing this issue. Thank you. I thought there was an error in it, so I've edited it slightly. However it now gives the total number in my column (but is quick) for each row rather than counting where the entry is 'Skill Achieved' in my 'Result' column. (Same result for each row)

This is my measure and it works fine where excel is the data source. (column names are slightly different of course)

Total skill numbers =
var selectedSite = SELECTEDVALUE('ListName'[Group]) //results from a slicer selection
RETURN
CALCULATE
(
COUNT
(
ResultsTable[Achieved skill]
),

FILTER
(
ResultsTable,
ResultsTable[Achieved skill]= "Skill Achieved" &&
CONTAINSSTRING
(
ResultsTable[GroupName], selectedSite
)
)
)

Example below of what I have/hope to achieve. My measure may not be correct, but seems to work fine for the excel data.. (I hope this makes sense)