only call aggregation code for local echo for relations

src/models/room.js

@@ -1106,6 +1106,7 @@ Room.prototype.addPendingEvent = function(event, txnId) {
         }
         this._pendingEventList.push(event);
 
+        if (event.isRelation()) {
             // For pending events, add them to the relations collection immediately.
             // (The alternate case below already covers this as part of adding to
             // the timeline set.)
@@ -1121,6 +1122,7 @@ Room.prototype.addPendingEvent = function(event, txnId) {
                     timelineSet.aggregateRelations(event);
                 }
             }
+        }
     } else {
         for (let i = 0; i < this._timelineSets.length; i++) {
             const timelineSet = this._timelineSets[i];