Always go through source tile change logic

src/ol/source/VectorTile.js

@@ -200,13 +200,15 @@ class VectorTile extends UrlTile {
     const minZoom = sourceTileGrid.getMinZoom();
 
     const previousSourceTiles = this.sourceTilesByTileKey_[tile.getKey()];
+    let sourceTiles, covered, empty, loadedZ;
     if (previousSourceTiles && previousSourceTiles.length > 0 && previousSourceTiles[0].tileCoord[0] === sourceZ) {
-      return previousSourceTiles;
+      sourceTiles = previousSourceTiles;
-    }
+      covered = true;
-
+      empty = false;
-    const sourceTiles = [];
+      loadedZ = sourceZ;
-    let loadedZ = sourceZ + 1;
+    } else {
-    let covered, empty;
+      sourceTiles = [];
+      loadedZ = sourceZ + 1;
       do {
         --loadedZ;
         covered = true;
@@ -268,6 +270,8 @@ class VectorTile extends UrlTile {
           sourceTiles.length = 0;
         }
       } while (!covered && loadedZ > minZoom);
+    }
+
     if (!empty && tile.getState() === TileState.IDLE) {
       tile.setState(TileState.LOADING);
     }