First off, because these leaves are so gigantic, every spot and every flaw is magnified.
I would love to see the whole tree so that I can really tell of the extent of what you describe. Is it the older leaves that are affected or younger leaves? Did this appear after you did the re-potting or was some of it present when you got the tree? Often there are things going on (leaf damage caused by trauma, excess sun exposure, root-bound, etc.) that resulted in leaf-lesions months before, but were mostly noticed after these lesions really turned brown and brittle.
I try to keep my fiddle leaf ficus plants moist all the time. They are heavy feeders and heavy water-users. I don't mean sitting the pots in water (you do want well-draining potting soil), but I try to water my plants every 2-3 days during the spring and summer months.
