Hi Andreza.
What do you mean by local one box? Do you mean something like this?
What you're seeing there, is usually called the knowledge panel. Usually the knowledge panel seems to pop up when Google either thinks the query is a brand search, or sometimes if there's no competition that's ranking well, it seems like they'll show it then too. I helped someone maybe 9 months ago that had a competitor that was showing up in that knowledge panel, and she wanted to know what she could do about that. We did other stuff too, but she knocked her competition off back into the 3 pack with her when all we'd done so far was verify and do a little optimizing on her GMB profile.
If you're showing that way for certain keywords, my guess is your business name is probably somewhat similar to those keywords you're showing for, and that you probably don't have steep competition in your city/industry for those keywords in the first place... or those are keywords that Google doesn't always show a 3 pack for in most cities anyway.
Making changes on your GMB profile can definitely cause a drop in rankings, especially if it's the wrong one. Google recommends using 'the minimum number of categories to fully describe your business'. Take a look at your competition, see what the ones ranking highly in high competition cities are using. I usually see 2~3 categories for most high ranking profiles in the industries that I keep an eye on at least, very rarely 4 or 5, and often just 1.
One of the map maker pros will need to weigh in on this, but in my novice understanding at least... it seems like changes to your profile will sometimes trigger a manual review in map maker, one of the volunteers will see it and 'okay' it. I don't know if just changing categories will do that, but if it does, there's maybe a chance that your profile had a problem with it that no one noticed, and then changing the categories called attention to your profile, and another issue was found? Not sure, but I suppose that's something I should get a better sense of.
Photos help ranking (as in, you should have photos) and high quality photos can help conversion (get more clicks and calls). As far as I know, that's about the extent of it. Seems like 5 photos is a good minimum to shoot for, 10 if you have them. Google will show two pictures by the way in the knowledge panel... a 'main' picture (not a logo) and an exterior building shot. Nice if you have both showing.
Anyway, hope my ramblings helped a little.