Yes, you can use Ctrl + C to copy, and Ctrl + V to paste, or right click on your layer, and select it there (where you can choose from multiple copied elements).
Or you can use the duplicating options too, which is next to the deleting icon for the layers, slides and sliders.
Your issue could be given by, if your text is resizing differently, then your image, also there is an align option at the layer’s settings:
https://doc.smartslider3.com/article/392-layer-settings-parallax-responsiveness
which is defining the responsive point of your layers, that if they should be positioned for example from the left side, or the center of the slider, and if these are different, that could influence this too.
Also this can’t be pixel perfect, because if the calculations are going like the text should start from 124.5px, and the image should end in 124.49px, a pixel can only be an integer, so a rounding has to happen, which would make in this case 1px mistake: 124px, 125px
In the full version we made an option to chain the layers together, and in that case, the layers are positioned from each other, and that can be more accurate, because in that case 0px is 0px.