Maybe I understood why it gave a page error.
my system changes IP frequently so if I have appinventor with the screen open and I try to create the Apk, the error page often appears, the reason is simple at least from what I understand: I should restart appinventor at the change of IP because it has to ask me again to log in as it doesn't recognize my system. In fact, if I restart appinventor everything goes fine, same thing if appinventor is not on the screen when I change IP.
as regards the buttons that do not respond to the code, here too I think I have understood what happens, when I make the changes by replacing the buttons with clickable images, in some cases it depends on the writer, who without realizing it by clicking on the properties thinking of be in the component that must receive the change, therefore a new property, I insert this property into the previous component that I had clicked a few seconds before which was still selected, not realizing what had happened by moving on.
In other cases, for some reason pressing the image buttons is perhaps less fast and if a timer is set with a few tenths of a second, with the normal button everything proceeded for months without errors, with the image button the modification of the content of the component took place late, not allowing the other timers to operate in time, in fact it was enough to increase the response time from 500 to 1000 i.e. one second and everything was fine.
I hope that's really the case. For now I have solved everything and everything works.
Greetings to everyone and thank you, above all sorry again for the time I have made you waste.