drag and drop bug

I want to create a phone system with apps that can be opened and moved via drag and drop.
I have the blueprints WB Phone (main phone widget), WB Screen Base, and WB App Button. WB App Button have the events on mouse button down and on drag detected.
In WB Screens, I want to move the children (WB app button) using the on-drop event.

Now, to my problem. If I integrate the WB screen into the WB phone with an anchor like mid, the drag-and-drop logic doesn’t work. I can only swap apps from row 1 with row 2 once after this on-drop is no longer called. However, it works perfectly fine in other rows or columns.

Then I discovered that if I set WB screens in WB Phone to Anchor Fill, the drag and drop system works everywhere. But depending on the screen size, WB Screens then slides out of the phone.

It looks like the minimum width for widgets to work in the grid panel for drag and drop is 360px. Is that possible? Or can it be even smaller?

What could be the problem? And how can I fix it? Thanks in advance