Created another map BP_Prototype2 along with other asset duplicates to hold my version of the prototype that I made earlier and couldn't commit cause of a merge conflict. Here's what I changed/addded to that version of the prototype:

Bubbles will now disappear on pop and reappear after a set time controlled by a var in BP_Bubble.
Min and max delay between bubble pop and next bubble getting highlighted can now be controlled using vars in BP_BubbleGrid.
There are now materials for bubbles in Content/Materials (default and highlighted). They are a bit transparent and glow slightly (although in the dark you can't see the transparency).
The scene is now darker and more simple to see bubbles better.

Config/DefaultEngine.ini

@@ -132,7 +132,7 @@ DefaultGraphicsPerformance=Scalable
 AppliedDefaultGraphicsPerformance=Scalable
 
 [/Script/EngineSettings.GameMapsSettings]
-EditorStartupMap=/Game/VRTemplate/Maps/VRTemplateMap.VRTemplateMap
+EditorStartupMap=/Game/Maps/Prototype_BubbleGrid2.Prototype_BubbleGrid2
 LocalMapOptions=
 TransitionMap=None
 bUseSplitscreen=False
@@ -141,7 +141,7 @@ ThreePlayerSplitscreenLayout=FavorTop
 FourPlayerSplitscreenLayout=Grid
 bOffsetPlayerGamepadIds=False
 GameInstanceClass=/Script/Engine.GameInstance
-GameDefaultMap=/Game/VRTemplate/Maps/VRTemplateMap.VRTemplateMap
+GameDefaultMap=/Game/Maps/Prototype_BubbleGrid2.Prototype_BubbleGrid2
 ServerDefaultMap=/Engine/Maps/Entry.Entry
 GlobalDefaultGameMode=/Game/VRTemplate/Blueprints/VRGameMode.VRGameMode_C
 GlobalDefaultServerGameMode=None