In Subnautica you may get grainy textures (where small squares break up the UI e.g Food Bar, Thirst, Health and so on...) which generally make it really difficult to play the game. Well let's get to how to fix this annoying bug. Its because of your resolution, so in order to fix it you need to (upon running Subnautica, the start window with all the resolution and input options) first make sure your game is windowed and the graphics set to "Recommended". Now run the game. If the UI is now working correctly (which I assume it does), save and exit the game. Then run the start window again but untick the "Windowed" option and then making sure your screen resolution matches your screen size. Upon entering the game (the one you just exited) the UI should no longer be grainy!

This sometimes occurs when the game texture quality isn't in tandem with your resolution settings. All you need to do is press f3 (which brings up the debug menu) then press f8 (brings up the feedback window but also gives you a cursor) and click on "Texture Quality" and select 3.

Wait for the game to finish changing all the textures and voila!

If this does occur, first send a bug report via f8 (feedback menu) and make it in as much detail as you can (it really helps the devs out) and if you want a quicker fix first open f3 (debug menu) then change texture quality to 1 and wait for it to adjust, then change it back to your original setting (basically, the good ol' on and off trick) and this may refresh your textures. If this doesn't work, it means your game may be corrupt or the game didn't install properly or update properly.

You can easily help me out by letting me know if I have missed anything out and that if any of your friends or other people get these issues, tell them about this guide! Thanks for reading this guide-of-sorts!