What causes a stem to disappear (see attached png)

When re-opening a previously edited file, I suddenly find a stem missing. See the attached .png file.

What causes that?

The score file is also attached.

There's also another sudden problem: staccato marks are now too close to the note. When looking at the "Articulations, Ornaments" style, I see that the spacing values of 1.0, 0.5, 1.0 have somehow reverted to the old values (0.5, 0.25, and 0.5).

How would that happen if I edited this file just a few days ago using build 5470 (v. 1.2)?! Note that this is the only version I have ever used.

It seems to me that the design of how styles and style references are stored in the score file needs a rethink. Either a link to a saved .mss file (e.g., the HTML equivalent of <link type="text/css" rel="stylesheet" href="my-style.mss" , or embedding styles (just as is done with CSS, <style>...</style>) would seem to be a better design than the current one which simply references style numbers.

But that may be something which requires a separate discussion thread.