Help with repeating returned values using index match

I am having to do a lookup against two sets of data and pull over information specific information from a column when there's a match. Typical index match usage really.

My formula works fine as it provides the correct return for the first entry, however when I use autofill against the rest of the rows the same return value from the first row is repeated. The formula itself works fine as when I select a column which has got the repeated returned value, click in the formula bar and then hit enter it will correct and provide the correct value for that specific row.

Does anyone know what may be the cause and how I can correct this?