This is a big topic. Are you using Runtime Virtual Textures? Are you using streaming virtual textures with your landscape? The fact that you’re using virtual textures would indicate you’re not using either RVT or SVT and this is why you’re getting blurry textures. Your framerate is likely to suffer greatly as well.
AFAIK, virtual textures don’t work in the main render pass for landscapes. I know with 100% certainty they don’t work with RVT. Without RVT, I don’t think it works either, but not as certain.
Let us know if you’re using RVT and/or SVT.