Not able to see other partitions in ubuntu file manager with GParted running

When GParted runs, all the partitions get hidden in the file manager (happens in most file managers, an exception being Thunar).

I can see that GParted is running in the second screenshot, and maybe that's why you cannot see them anymore in your file manager (you said that you could see them initially).

You would most likely be able to access them after closing GParted.