Hello - so, there are naked edges in the object, you can locate these using ShowEdges. What this means is that the edges of the various surfaces are too far away from one another in those location to Join at the current file tolerance. The ‘middle’ surface on either side needs to be matched (matchSrf) to the surfaces above and below it:
ExtractSrf that surface and Untrim it, then MatchSrf for Position or tangency to the edges of the neighboring surfaces. You will need to use the ChainEdges option for selecting the target surface edges. See Help on the MatchSrf command - you’ll also need ‘Match by closest points.’