The mesh can not be found.
DynDOLOD tries to not generate LOD for or with missing assets to avoid issues.
In the worst case scenario missing meshes cause CTD. Typically missing meshes cause red triangles with an exclamation mark for missing meshes. In the best case it just means a missing LOD asset, so something won't have a LOD representation.
The log tries to only report missing meshes in case they might actually be used in the game. Mods sometimes contain orphaned or unused records or data, which is not causing problems directly.
If a mesh is required or not can be verified with xEdit. Look up the mentioned base record and check the Referenced By tab at the bottom of the right record window. Then check if the base record is used by references in worldspaces or cells that the player can actually reach in normal game play. Plugins sometimes contain test worldspaces or cells, so if a missing mesh is only used in them, it is not problematic for a play-through.
If it has been verified that the mesh is not required, try to remove or update the unused record/entry so the non existing filename is not being referenced.