The Piano Overlay has slightly narrower keys than a standard piano, and the white areas between the black keys are especially narrow, so we have seen this before. It isn't expected behavior, but it can happen, depending on the individual, how they play, and the shape of their fingers.
First thing's first. Let's make sure that your Morph and overlay aren't dusty, as dust can cause false touches. You can wipe the Morph with a cloth (microfiber is best, but not necessary), and then rinse the back of the Piano Overlay under water and dry it. If either of them were dusty, that might do the trick. The easiest way to tell if you're getting false touches is by looking at the LEDs on the Morph itself. You'll easily see if you're pressing a white key only, and the black keys are also triggering.
Next, let's try to increase the Threshold of the black notes. The Threshold determines how sensitive the areas are, and by increasing it, you decrease the likelihood of false touches. So you'll want to go to the Sensel App, Ctrl+click or CMD+click all the black keys (like in the screenshot below). The default Thresholds for the MIDI and MPE mappings is 4, so try 7 perhaps? If that solves the false touches, then you can try 6 or 5, and see if that's enough. If not, then go up to 9 and see if that solves it. If you find a threshold that works well for the black keys, you can then apply that same threshold to all the white keys as well, if you want to make all the areas uniform. You easily do that, use Ctrl+A or CMD+A to Select All.
If you're continuing to have issues after taking these steps, please email email@example.com