I checked to make sure it wasn't any resource packs I had installed by disabling all of them, however the issue still persisted.
I'm currently using 2.7.1 version 1.16. I have also maxed out all graphics settings on my computer, to fancy.

I had the same problem when my graphics were set to fast. But you said you are on fancy?

I also get this problem sometimes, mostly because of texture pack changes. Just restart the game and it should be fixed. If not, reinstall everything. does your optifine version match with the forge one?