I logged on to a server and loads of random textures are missing but on the inventory, they aren't. I am not using a texture pack. On singleplayer this happens as well, but more textures are there. The missing textures (the ones that affect both multi and singleplayer) are:

Bone Block, Nether Brick Stairs, Purpur Pillar, Doors, Wooden Stairs and Cut Red Sandstone.

I think there could be more but it is incredibly difficult to find them because you can actually see them in the inventory but not when placed.

These are the blocks that have lost textures on both multiplayer and singleplayer