I watch a lot of YouTube videos of RotBP and I noticed that new players playing online multiplayer on the Short Fused map, second phase, often don't realize that A) They can destroy the extractor, but most of all B) How many times they have to blow it up.
When they realize they have to get Aleph to charge it 5 times I notice they begin to do this in pieces without first destroying the extractor to buy time while they get a full stack of 5. I believe this is because they have no idea how many times they have to blow the extractor up because there is just one yellow line up top with no indication of how many times.
My suggestion would be to add lines between each extractor health segment on the extractor health bar at the top to indicate to players how many times they have to perform the action. This will give new players a sense of the scope of urgency and will get them to understand they need to build stacks and/or destroy the extractor.