Placing GuiObjects under a folder inside a ScreenGui makes the UI Editor error and you are unable to use the editor to modify said objects.
This bug can be replicated by having a ScreenGui, inserting a folder inside and inside the folder adding any GuiObject (TextLabel, TextButton, etc).
Can reproduce this.
I was about to make a thread for this issue, but did a quick search and found that this exists.
It’s really strange that we still have this issue after so long.
I discovered it while trying to implement folder support to my SmoothScroll module, which incidentally had the same issue as the UI Editor.
The error is simply that it tries to index the .AbsoluteSize and .AbsolutePosition of the GUI’s .Parent instead of indexing it on GUI:FindFirstAncestorWhichIsA("GuiBase2d"). Should be a rather simple fix, unless there’s something in the editor that I’m not aware of.
Ooooh yeah, this is extremely annoying considering I like to keep things tidy when it comes to everything. This thing has held me back from using folders when it comes to both UI design and editing.
It does appear that it only checks the .Parent value without even checking is it a UI Object as said by @boatbomber.
I have this problem as well. It is quite annoying.
I wanna say that even this is still happening, and it is irritating.
For roblox developers: Why don’t they simulate that the frame in the folder is the children of the parent of the folder? This error ruins my ability to have my frames / guides organized. It’s unreal that developers are not fixing this issue 2 years later.
This is still an issue and makes using packages to share UI with multiple places unusable. When ScreenGui is placed inside a folder elements can still be resized but can’t be moved.
To navigate around this bug try adding your folders after you have already edited your objects. If you need to edit things later in a folder you can just take those items out, then edit, then put them back in.