for a couple of turns the battle previews have just stayed like this 

I also see this very frequently. Saving and reloading fixes it, but it is clearly bugged.

Yes, i can confirm this does happen occasionally.  The reason i didn't report it yet is that i did not manage to come up with clear instructions to reproduce, see https://www.games2gether.com/amplitude-studios/humankind/forums/171-bug-reports/threads/38271-guideto-reporting-bugs-with-the-lucy-opendev?page=1#post-307813

The best i can come up with is this:

Steps to Reproduce:

1. Have some unit selected.

2. Move your mouse around the screen, in particular on and off other player's assets like units and fortifications.

3. Sometimes, after moving the mouse off the ememy asset, the battle preview remains active and there is no way to get rid of it short of reloading the game.

4. Sometimes and even more rarely, in addition to what i described in step 3, the unit you had selected in step 1 becomes completely invisble.  You can still select it (even by clicking on the hex square it occupies but where you can no longer see it, or using the unit list), you can move it, merge it with other units, attack with it etc. etc., but the unit picture is no longer shown on the map, not even after moving the invisible unit multiple times.

Reproducibity: 1/5, very inconsistent

I think the bug is more likely to show itself when the unit selected in step 1 is standing close to enemy fortifications, but i'm unsure, and that's probably not the only situation it happens.

Quoting a likely useful suspicion voiced by the user "Oldtitans" in this other thread :