This hole is created because the vanilla terrain loading can't keep up
It is expected behaviour from DH side as DH can't know if a chunk is loaded or not, because getting this info differs significantly between MC versions, Sodium versions and Optifine versions.
Having so many different code paths would be hard to support and very bug prone.
There is however dynamic overdraw feature in current DH nightly that moves the circle closer the faster you move to reduce this hole