IF YOU ARE EXPERIENCING ANY OF THESE FOLLOWING BUGS OR ISSUES, HERE ARE THE MOST COMMON REASONS AS TO WHY AND HOW TO FIX THEM

BUGGED CHEST MODEL
If ur chest appears bugged with it's textures, update your optifine to G8 and above! 
Why?
Most common reason as to why this issue happens is because of an outdated optifine client


MODDED BIOMES APPEAR WHITE, AKA WHITE COLORMAP FOR MODDED BIOMES
If you are playing on a modded client with modded biomes added and they appear white, download the "Reimagined Colormap Fix" addon here: https://www.planetminecraft.com/texture-pack/reimagined-colormap-fix/
Note this only works for optifine users, since this is an optifine related issue afaik
Why?
Most common reason as of why this happens is because the pack primarly uses optifines colormap feature, which allows for a much more in-depth control of all kinds of colormaps for all blocks, like water colormap, sky colormap and so on.
Sadly, it seems as if optifine hardcodes this, so any biome that you have not customized, will have a "missing" color, aka will appear white.
Turning overwriting the colormap, makes it revert back to the vanilla colormap, or at least the texture pack reverts back to it's own custom vanilla colormap. So still a new texture pack colormap, just not a optifine colormap. 


THIS MODEL DOESN'T WORK, OR THIS FEATURE DOESN'T WORK!
Check if you are playing on a client with optifine installed, if not, you guranteed be missing some of the packs features, such as randomized mobs, 3D chests, biome specific blocks, etc
Why?
Vanilla minecraft sadly have a lot of limitations as to what texture packs can modify and change, luckily optifine offers a lot more freedom to texture pack makers, but optifine is required for them to work!


-Reijvi