Constant save error & more

I have already posted several topics on this 'saving error' on MS4. If you [save] or [Ctrl + S] a score, there's a high chance that '~ file is corrupted' error message is seen. So I have been utilizing two ways: 1. if you [save a copy] there's chance that the copied file opens without problems. 2. I use a zipping/decompressing program to restore the file(which was saved by [save]). When I use the program and decompress the mscz file, it prints out that Header of the file is damaged, and can be recovered. Proceed? If I proceed, a repair file (mscz) is made and the file opens without problems. Have been mainly using the latter method b/c it always worked.

But today this happened: I saved a file by [save], opened it, saw the corrupted file error, decompressed as mentioned above, and got this.(see attached img)
How can a saved .mscz file not contain a .mscx file? Until today, it was same but .mscx file existed every time.

I almost know nothing about extensions and musescore software. Wonder if this thing happens to other users. Please fix whatever issue is going on with the saving process. And please help restore the mscx file. (I have looked up for mscbackups and it was a really old version of the score.) Thank you.

Editing and another bug caught: [Shift + ,] [ stuff ] [Shift + .] -> whole thing doesn't appear