I started a process with GUI from the command line in a remote computer using ssh -X. Knowing it would take a long time to run it, I left it in the background and disowned.
As I feared, I had connection problems before it ended and got a broken pipe. After I was able to reconnect, I used reptyr to recover ownership of the process. So far, so good. But is there any way I can reopen its GUI now that I own the process again?