extruded hole blocked by unknown artifact

I am new to this program and have become stuck with an issue. I extruded several holes through an object, one of the holes has some kind of artifact on the bottom plane and seems to be “tied” to a corner nearby??? See screenshot for more details.

Any help would be appreciated. I have tried to delete the hole, I have filled in the hole and re-extruded it only to have the same thing show up.

Thank you in advance.