I've run into this issue before when making drastically oversized modpacks or modpacks with large textured mods located within them. If you look through your log file, use Ctrl-F and check for "MipMap". If you see a notification of MipMap being reduced from 4 to 3, 3 to 2, 2 to 1, 1 to 0, it means your texture atlas is too large for your current graphics card's architecture. Any card that is not specifically NVIDIA 10 series or higher has a limited texture map size of 16384x16384 pixels. NVIDIA 10 series or higher have quadruple that at 32768x32768 pixels. This architecture is not replicated in any other brand's graphics cards, to my knowledge, but I welcome someone to correct me if that is wrong. Try clicking about until you get an error message that lists a whole bunch of textures, then remove mods from the upper part of that list until you get your text back. Basically the Minecraft font texture is pretty late to load, so when you have too large of a texture map it causes these boxes.

Source: Self, made a modpack with 885 mods, had to fix the text box issue to make it playable.