How is this a problem? What if they are already well known and they are fully aware of that, that is why they stop doing promotions for a while to spread their names more evenly. I think what you really mean there is if the project stop on developing and improving. That will looks suspicious as an investor.
If you notice that, then it can be a good sign to move away from the other active projects before it's too late. Project that can survive a couple of dumps or bears doesn't mean they are still a great project to invest in. There are lots of them but they aren't really that profitable. This is why many of us are looking forward to a new coin because their hypes are still fresh. We only need to be careful though.
Sometimes a project may use a lull in development for the purpose of manipulation. Holders will see that the project has lost its former activity and may decide to sell their tokens because of this, and after the team collects most of the tokens, work at the project will continue and the price of the token will grow very well. But if the project has gone through several cycles but still has not achieved any significant result, then most likely you should not expect great results from it.