Here is a diagnostic tree for brown spots on leaves. They can have many sources, sometimes more than one at a time:
- spots are on every leaf, newer and older:
- check for sunken spots or dead areas showing rings of growth => advanced virus/bacteria/fungus
- can be an outside factor like pesticide spray, chlorine heavy misting
- spots only on older growth
- can be over watering, check to see if dead areas are still moist
- can be under watering, dead areas usually occur on tips and area is dry
- can also be a virus/bacteria/fungus that is just getting started
- can be physical damage from crushing or freezing
This plant looks very healthy. I would not worry about the dead spots unless the whole leaf dies off. Check that your watering is following best practices. Let the top half inch (1 centimetre) dry out and then water thoroughly until water runs out the bottom of the pot. Do not water again until the top part of the soil is dry.
Edit: I looked at your second photo. It does not look like physical damage. Remove the leaf and watch for further occurrences. Watering practices are a common cause of virus/fungi/bacteria. Consider letting the plant dry out before watering again as indicated in the previous paragraph.
If you are removing dying leaves always try to remove them cleanly where they join the stem