I use nodebb 1.7.5 and on one evening playing around with it on my phone I wondered why there are 2 search icons. So I thought, maybe there's one builtin search and one plugin. I went into admin and disabled the search plugin to see what happens.
Now, both search icon disappeared, but my skin and theme settings went away as well! I have a global setting for skin: slate and theme: persona. After the search plugin was disabled, defaults were used (lavender and some white bg skin). I was unable to change this. In the skin settings, for example, I could set the skin to slate, apply it, go to frontpage, shift-reload - nothing changed. Same for theme. Also the current skin in use was not being shown in the settings. I also tried to restart nodebb multiple times to no avail.
Finally I re-enabled the search plugin and voilà - slate and persona reappeared as if never something weird has happend.
PS: the 2 search icons are only visible in mobile view, in a browser there's one menu icon and one search input box. The latter turns into a second icon in mobile view. I think this is a bug in the slate skin, but I'm unsure and I can live with it