Since it is a piece of spring steel, and tempered so that the sides act as springs, one guess is that age has weakened the temper. Or else wartime quality standards and materials slipped.
The cover and the loaded-chamber indicator do not affect safety or functionality, but it's a bit puzzling to see something fly off the top of your weapon, and look down into the slide and see an empty area that used to have stuff in it.
Understand ......and I hate seeing parts missing or flying through the air as well. Bad day if you were to lose such from a treasure such as that connected with family history.
I have a Krag Carbine, 30-40 (30 army) that my grandfather used as a teen in Colorado . He was childhood friend of the boxer Jack Dempsey. They rode fence together and my grandfather carried the Krag Carbine. I treat that like a precision piece of tooling. Carefully reload for it and have had NDE performed to see if I need to hang it on the wall before it self destructs. I still get a Mulie with it every year. My treasured firearm with history of it’s own.....:o)