I am doing buckling analysis using Advanced Solver and get the buckling factors. I have a number of load items in a load case. So how do I know which one needs to be multiplied by the buckling factor to get the buckling load. Also as I have multiple primary loads and REPEAT LOAD cases, am I not supposed to get different buckling factors for different loads ?

The buckling factor is applicable on all the load items within a load case. So with the current arrangement of the load items within a load case, this is the factor by which you need to multiply each item to get the structure to buckle under the total applied load. For all primary loads ( including REPEAT LOADs ) you will get separate buckling factors. The GUI will only show the results for the last primary load case but you can find the ones for the prior cases within the analysis output file.