Before anything else,
@BeKind, please take a few moments to go into your "Profile" and update it, giving your city/state and/or USDA zone. That information will then be shown in the upper right-hand corner whenever you post. Knowing where one lives is important when discussing plants.
Typically, Fiddle Leaf Ficus have little pest problems, probably because their leaves are so thick. I will guess your problem is stress-related and due to one (or more) of three things, water, light, or drying-drafts.
Generally, because these are trees, they are extremely heavy "drinkers" and have fast growing/spreading roots. Your plant may be root-bound and thus, when you water it, the water runs pretty much straight through without truly wetting the roots. The only way you will know whether this is the problem is to un-pot the plant and check the root-ball. It may be time to up-pot your plant. Temporarily, if she needs up-potting but you cannot do so, put the entire pot into a large bucket or deep sink filled with water. You want to cover the entire root-ball with water and let the pot sit in the water for an hour. Then let drain and put it back in its saucer or on the floor. Do this weekly until you can up-pot. Be sure you use well-draining potting mix when you do up-pot and go to a 4-6" larger pot.
Your plant may be getting too much direct sun on some leaves or even parts of leaves and this can sunburn those leaves. Early morning or late afternoon sun is fine, but you really don't want sun coming through a window/glass door to strike the leaves between 11:00 AM and 3:00 PM.
You plant could be in a draft from a heat vent. Hot (or even warm), dry air from vents, blowing on particular leaves, can dry those leaves fairly rapidly and causing tissue to dehydrate and die. When our AC runs, the cool, dry air will do the same thing.
That's the best I can come up with at the moment. It could be one, two, or a combination of all three things going on. Fiddle Leaf Ficus should never have leaves that die back like this and generally is a sign of stress. You'll just have to do a bit of detective work. Good luck.
By the way, do tell us what you find when going through those three steps of investigation and your remedy(s).