Sometimes LittleTiles Blocks doesn't load corretly.
Like this:

When i press F3+A for reloading chunks LittleTiles Blocks load correctly at the first time
Like this:

Some Data:
LittleTiles Version -> LittleTiles_v1.5.20_mc1.12.2

LittleTiles sometimes requires some time to load all blocks. You can use the command /lt-debug to see how many blocks are in the rendering queue. Besides that there are some mods which cause rendering glitches like Phosphor.

Also make sure to update to the newest version.