Its probably due to,when an part is resized,it isnt able to touch anything,but after stopping it,it may be touchable once again.(You can probably see this on building type of games.)
“This event only fires as a result of physics movement, so it will not fire if the CFrame property was changed such that the part overlaps another part. This also means that at least one of the parts involved must not be BasePart.Anchored at the time of the collision.”
We aren’t 100% sure what you are trying to achieve, but the best thing to do would be to calculate the end size of the sphere before resizing it. You can raycast from the center of the sphere to get a final radius.
It depends what you want to achieve. For example you can loop through all the parts and check if their position satisfies the condition
(x - x0)^2 + (y - y0)^2 + (z - z0)^2 <= R^2
where x, y, z is the position of the part, x0, y0, z0 is the center of the sphere and R is the radius of the sphere.