I have had this happen several times, but now I think I know what is going on.
When you use a Glide Table, deleting rows is a bit hit and miss (it seems). So you are not sure if the row is deleted or not. It is easy to press delete more than once.
Then you go back into the UX designer…
And I find that, in one of my tabs (not sure the logic which one), the design components (starting from the top) have been deleted.