Go to the installation folder of your copy of Minetest (where the ''bin'', ''builtin'', ''games'', ''mods'', etc. folders are). Find the file ''Minetest.conf'' - not minetest.conf.example, but minetest.conf - the one with only a few lines, and no ''#'' symbol before any of them. Add this line:
Your phone or window isn't wide enough to display the code box. If it's a phone, try rotating it to landscape mode.
This will disable the texture atlas, and the problem will be fixed. But - be aware that this causes a minor drop in graphics performance. If you have a low-end PC, it will cause a significant drop in framerate.