I created a module that creates GUI components on the fly, and I’m using it to create frames based off of items in a backpack.
For testing purposes, i’m clicking a button to add the frames into the main frame.
Not that its important, this is how i’m creating the GUI frame
gui:Build('Frame',game.StarterGui.Backpack.BackpackUI.MainFrame)
frame being, well, the frame. and the second parameter is the parent of the frame.

as you can see, the frames are being added but nothing is popping up on the main frame.
Even without using my module, when i just copy and paste a frame into the main frame with the uigridlayout, nothing happens. However, if i do it when im not in game, it works perfectly. Whats causing this?