welcome to photrio.
there is an effect with b&w film where gross overexposure can lead to a reversal effect. If the large gray area is what has you confused, it could be from a severe sustained light leak going into reversal. Hence the normally exposed sky looking white and the central blob being darker.
A good way to find a leak is to put the film in the camera as shot and see where the leak area is. And be aware that often the actual leak is before or after the exposure opening, when the film is coming off of or going onto a spool. So look at. frames before and after the film gate, also.
Light leaks, decayed foam and such, are common on older cameras. Hopefully this will be resolved quickly and you can enjoy your present.