Also galleries that were fine pre-UCP now don't organize images that neatly: https://battlefront.fandom.com/wiki/Darth_Maul#Gallery From the looks of things, this only affects those galleries have center-aligned captions (<gallery captionalign="center"></gallery>). Not too familiar with UCP changes regarding galleries, so is there some sort of new syntax for galleries that causes this glitch?
For the tabbers, I think it might be something in the wiki's JS that is causing this. I loaded the page without any wiki CSS/JS and it didn't behave as you described. However, it does when I allow the page to load all of the wikis custom CSS/JS. I can try to look into it more if you need me to.
The gallery issue is known and is the result of the global gallery CSS not loading for some reason. I don't know if/when Fandom will fix it but, in the mean time, you can just purge the page. I have already done that for the example you linked to. If you check it now, it should display properly.