Cross-beam issue: beams come and go with the slightest change to unrelated parts of a score.
Load the fragment score i've attached, the select the "stacc." at the botton left, and move it down a minimal amount. Now look at systems 2 and 3. You should the beam disappear in bar 9. divertimento-test.mscz
See https://musescore.org/en/node/290055#comment-923511 for a discussion of this issue.