different fix for clustering, this one should work :) (sounds familiar)

dist/vis.js

@@ -34394,36 +34394,14 @@ return /******/ (function(modules) { // webpackBootstrap
             if (this.body.edges[edgeId] !== undefined) {
               var edge = this.body.edges[edgeId];
 
-              // if the edge is a clusterEdge, we delete it. The opening of the clusters will restore these edges when required.
-              if (edgeId.substr(0, 12) === 'clusterEdge:') {
-                // we only delete the cluster edge if there is another edge to the node that is not a cluster.
-                var target = edge.from.isCluster === true ? edge.toId : edge.fromId;
-                var deleteEdge = false;
-
-                // search the contained edges for an edge that has a link to the targetNode
-                for (var edgeId2 in childEdgesObj) {
-                  if (childEdgesObj.hasOwnProperty(edgeId2)) {
-                    if (this.body.edges[edgeId2] !== undefined && edgeId2 !== edgeId) {
-                      var edge2 = this.body.edges[edgeId2];
-                      if (edge2.fromId == target || edge2.toId == target) {
-                        deleteEdge = true;
-                        break;
-                      }
-                    }
-                  }
-                }
-
-                // if we found the edge that will trigger the recreation of a new cluster edge on opening, we can delete this edge.
-                if (deleteEdge === true) {
-                  edge.edgeType.cleanup();
-                  // this removes the edge from node.edges, which is why edgeIds is formed
-                  edge.disconnect();
-                  delete childEdgesObj[edgeId];
-                  delete this.body.edges[edgeId];
-                } else {
-                  edge.togglePhysics(false);
-                  edge.options.hidden = true;
-                }
+              // if this is a cluster edge that is fully encompassed in the cluster, we want to delete it
+              // this check verifies that both of the connected nodes are in this cluster
+              if (edgeId.substr(0, 12) === 'clusterEdge:' && childNodesObj[edge.fromId] !== undefined && childNodesObj[edge.toId] !== undefined) {
+                edge.edgeType.cleanup();
+                // this removes the edge from node.edges, which is why edgeIds is formed
+                edge.disconnect();
+                delete childEdgesObj[edgeId];
+                delete this.body.edges[edgeId];
               } else {
                 edge.togglePhysics(false);
                 edge.options.hidden = true;

lib/network/modules/Clustering.js

@@ -380,37 +380,14 @@ class ClusterEngine {
         if (this.body.edges[edgeId] !== undefined) {
           let edge = this.body.edges[edgeId];
 
-          // if the edge is a clusterEdge, we delete it. The opening of the clusters will restore these edges when required.
-          if (edgeId.substr(0,12) === "clusterEdge:") {
-            // we only delete the cluster edge if there is another edge to the node that is not a cluster.
-            let target = edge.from.isCluster === true ? edge.toId : edge.fromId;
-            let deleteEdge = false;
-
-            // search the contained edges for an edge that has a link to the targetNode
-            for (let edgeId2 in childEdgesObj) {
-              if (childEdgesObj.hasOwnProperty(edgeId2)) {
-                if (this.body.edges[edgeId2] !== undefined && edgeId2 !== edgeId) {
-                  let edge2 = this.body.edges[edgeId2];
-                  if (edge2.fromId == target || edge2.toId == target) {
-                    deleteEdge = true;
-                    break;
-                  }
-                }
-              }
-            }
-
-            // if we found the edge that will trigger the recreation of a new cluster edge on opening, we can delete this edge.
-            if (deleteEdge === true) {
-              edge.edgeType.cleanup();
-              // this removes the edge from node.edges, which is why edgeIds is formed
-              edge.disconnect();
-              delete childEdgesObj[edgeId];
-              delete this.body.edges[edgeId];
-            }
-            else {
-              edge.togglePhysics(false);
-              edge.options.hidden = true;
-            }
+          // if this is a cluster edge that is fully encompassed in the cluster, we want to delete it
+          // this check verifies that both of the connected nodes are in this cluster
+          if (edgeId.substr(0,12) === "clusterEdge:" && childNodesObj[edge.fromId] !== undefined && childNodesObj[edge.toId] !== undefined) {
+            edge.edgeType.cleanup();
+            // this removes the edge from node.edges, which is why edgeIds is formed
+            edge.disconnect();
+            delete childEdgesObj[edgeId];
+            delete this.body.edges[edgeId];
           }
           else {
             edge.togglePhysics(false);