Generally, you should include:
What went wrong? The umbral blade will tunnel through the ground and explode underneath in areas with a lot of mild elevation changes. This will cause the blade either to tunnel until it hits a solid object, or where it thinks the targeted mob is instead of the ground location as should/would be. This is inconsistent behavior and happened the most in the dried lakes areas in Act 3, in various locations all over the map.
Log File I do not have any videos or screenshots
Screenshots (via a site like imgur) or video, if applicable
Thanks!