How to compare 2 layers in Ax?

I use the “compare” tool to show differences between the Xpo i m tyring to import and the VAR layer (we do all customization in VAR). Sometimes wen using the compare tool ( the pull-in/pull out icon that is the black colored arrow) does not show…What can be the reason?

How to make that black colored appear wenever i m importing?Pls help