G4P gui builder latest version doesn't work with older sketch

Updating an older complex sketch I found out that the latest G4P gui builder is not compatible anymore. I installed an earlier version of the tool which works for now.
Question is: is there some way to convert the ‘older’ gui to one that will work with the newest G4P gui builder? To remake the whole gui is a lot of work. I might go to ControlP5 if that is more stable and backwards compatible.

Unfortunately not see this webpage for more info.

GUI Builder is a tool for designing GUIs using the G4P library and has nothing to do with finished sketch.

Both GUI Builder and G4P are as stable as ControlP5 whatever you might think. By all means use ControlP5 as a replacement for G4P but as far as I know it does not have an associated GUI design tool. If I am correct you would still have to modify the GUI layout by hand.

My usage of the word ‘stable’ is not correct, you are right. I meant future proof. For which backwards compatibility is quite important in my view.

G4P is backwards compatible for all sketches created with Processing 3 or later, and AFAIK so is ControlP5

G4P but not Gui Builder right?

Correct, GUI Builder has limited backward compatibility because it uses Java serialization to store the GUI data