2D or 3D ? (3d objects may show as a problem, but can still be used without problem)
At the top of selection palette one can click filter and by audit, to show just the problem objects. These can usually be clicked on the show the position of the object,
though can't be deleted via selection palette.
As for Select by query, the extents typed into the query needs to be precise, unless one is using a condition. Are you reading the extents from the selection palette. Say the objects has extents of 334.998795. one would use Select by Query, criteria - common properties - extents size. In the dialog, click the first line, then click it a second time to put in the I curser ready for typing. either type in 334.998795, or use something like (Value / relative / And-Or) 334.5 > And [on second line] 335 <