In resource packs with custom leaf blocks – i.e., models with additional elements, "bushy" leaves – mipmaps seem to add noise to these blocks. This can be observed on all levels of mipmapping, as well as both Fancy and Fabulous graphics (Fast also may produce the same issue, but it's far less noticeable due to "bushy" leaves already being unable to render on Fast graphics). These artifacts seem to occur primarily in the direct vicinity to the player, falling off both at the edges of the player's vision and as leaf blocks grow more distant.
Can you provide the resource pack used in order to reproduce this issue.