What do you mean that you "lose styling and visibility setting" of the group? For the existing controls in the group, or for the newly added elements? If the former, then that would be a bug. If the latter, then it's how groups work - a group is a construct to allow you to set multiple properties .
For example, if you have 3 labels in a group, and after selecting the group you set the color to Red. What that action did was to set the color to Red for all three individual controls; the group itself doesn't have a "color" by itself. Now if you insert a fourth label into the group (by selecting the group, the label, and then grouping them again), you're creating a new group with all four elements (PowerApps doesn't have the concept of "nested groups"). All properties of the controls are unchanged, but if you set a property of the group, it will now apply to all 4 controls.
PowerApps doesn't have "group properties" because that can lead to conflicts. In the same case of the label, if the group had the color set to red, and the fourth label had it set to yellow. When we group them together, which color would "win"? Or if you're trying to combine two groups (each one with 3 controls), in case of conflicts properties of which group would prevail?
If you feel that having "group properties" is important, please consider creating a new feature request in the PowerApps Ideas board.
