First off, the go-to article to understand preventative and curative grub treatments, different products, and the different timing required for different products is the annually-updated article from Michigan State University:
https://www.canr.msu.edu/news/how_to_ch ... _your_lawn
I believe you will find that the article will give you the information needed to help you determine how you should proceed. I highly suggest you read the article. If it doesn't make sense to you, read it again a day later -- you'll pick up more on a second reading that didn't make sense the first time through. I reread the article just about every year.
I'm hesitant to even provide my quick interpretation, as you reading what I have to say isn't a very good substitute for taking the extra time to read the article.
However, rather than seem like I'm ignoring your question, here goes...
The grubs you are seeing now are likely relatively large, nearly mature grubs. They will pupate soon, and remain as pupa (like cocoons) for a few weeks, then emerge as adult beetles this summer.
The GrubEx you applied this spring will *not* kill those nearly-adult grubs. The pesticide is not sufficiently concentrated and potent to kill the nearly mature grubs. Rather, the GrubEx you applied recently is targeted to kill the grubs in the next annual cycle -- it will kill the baby grubs that will be hatching from eggs laid by the adults over the summer. Essentially, the product you applied this spring of 2019 will kill the new crop of baby grubs that would otherwise be eating your grass roots in the fall of 2019 and spring of 2020.
In order to kill the grubs in your lawn right now (which are going to be done eating in a few weeks and becoming adults) you would need to apply a curative product. Scotts GrubEx is not that product. The MSU article provides specific guidance for products to use for that purpose. A few grubs are tolerable by a healthy lawn.
The advantage of the preventative products is that they provide relatively targeted control (affect primarily only the target pests) and can be used at lower dosages, since they are killing baby grubs, not nearly-mature adult grubs. They do an excellent job of breaking the perpetual life cycle, and are sufficiently targeted and low-impact to the environment that they can be used every year.
Rather the curative products are relatively broad spectrum and will kill many other types of insect life in the soil (even beneficial insects), and require higher amounts of the active ingredients to achieve that effect. It's kind of the equivalent of deploying a "nuclear" insecticide to your lawn.
The good news, if you decide to apply a curative product this year, is that since you have also applied a preventative product this year, you shouldn't need to apply a curative product this fall or next spring.
What I do is apply a preventative grub treatment every year, because I had grub problems about 5 years ago. I still see some grubs from time to time (the preventative products do not eliminate 100% of grubs), but have not had any problems with grubs damaging the lawn since regularly applying a preventative product.