Firstly where is the door? purpose built flats? hotel offices??
Anyway the first question has been raised; is the window frame part of the door frame, if it is the 'hole' may have been a transom window, if it was then it may of had a piece of Georgian wired glass in it; would you be concerned if you found that in a block of flats? probably not because you have the 30 minutes FR and integrity.
An easy cheap fix when plywood has replaced FR glass is to put Georgian wired glass back in, with the correctly fixed beading, and then put the plywood or a piece of plasterboard/MDF over the glass/beading if privacy/decorating/painting is required.
Given the size of the 'hole' above the door a double layer of plaster board would be acceptable sealed at the edges mounted within good beading, depending what premises it is located in. If the 'hole' is on the larger size it may need some studwork to provide stability, if so board it both side.
Don't forget we accept notional fire resisting doors, well a fire risk assessor will and maybe not a fire door surveyor.