Improper use of island fields may lead to performance problems.

[Sony]

Hi, I have run document analyzer on my dashboard. I'm getting the error - 'The expression uses a Field from an island table. Improper use of island fields may lead to performance problems'. I have loaded data from 2 sheets from a data file in the following way:
LOAD 

(fields)

From lib://DatFolder/DataFile.xlsx

(ooxml, embedded labels, table is Sheet1);

LOAD 

(fields)

From lib://DatFolder/DataFile.xlsx

(ooxml, embedded labels, table is Sheet2);

Can anyone please help in resolving the issue.

Thank you!

[Or · Accepted solution]

This message means exactly what it says - one of your tables is not connected to any other table in your data model. When you use that in an expression, there is a possibility of it causing a major performance issue (as well as incorrect values) due to the lack of a join. If this is done intentionally, you can ignore the message. If it is not, you've probably missed the join between your tables.