I'm not sure how, but the leg on the short side of the desk has a width dimension the extends out from the desk making your empty space. Reload your original model and redo the leg. that should solve your problem.

Good Luck

Thanks, will take a deeper look so see if i can spot it. The left (shorter leg) is a duplicate of the right hand long end leg. Not quite sure what I did. Guessing whatever is wrong doesn't affect that leg because the desk extends beyond the problem area.

Might be worth redoing both legs if the right one is borked too.

As an initial test i just deleted the short end leg entirely and it resolved the issue.