This seems to be related to a previous divisi issue that you’ve encountered (From divisi a 2 to divisi a 3).
If I had to wager, the source of the problem seems to be the same in this case too, namely that: “If a divisi change is already in force at the start of the system, then that is the one that will take effect for the whole of that system. There is no alternative but to make the divisi to three parts start earlier, and/or change the system formatting so that the divisi to three parts coincides with the system break.”
Compound that with the condensing tool, and I would imagine it would give you precisely the results you’re seeing. (And correct me if I’m wrong, and not that this is particularly consequential, but it’s only that the first AND last label are shown if the last label is unis., yes? It looks like if the last label is div.—or perhaps if the first and last label are the same?— then only the first label is shown.)
Unfortunately, I don’t have a better solution than to suggest not using the divisi feature to merely mark divisi and unison. I’d just use shift-x text for that and limit my use of the divisi feature to only instances where I needed separate staves to appear in both the score and parts. I could of course be mistaken, but I get the sense that that is the way it was intended