In 64 bits, the window remains blocked

Hello, I moved a project from 2016r3 / 32bits to 2018r4 / 64bits.
Everything works fine except a window that blocks when opened.
It contains about 40 controls (4 listbox, 6 popmenu, 15 pushbutton …). On my screen the location of the window is gray and the window is not displayed at all and the app remains locked. With debugger, it happens at the end of the open and I can’t stop the program with the “pause” or “stop” button.
If I compile in 32 bits with xojo2018r4, the window opens.
What can I try?

In a listbox, the new xojo 64bits does not check the old value of the scrollposition before assigning it again -> it causes looping list refreshes
Solution: Test the value of the scrollposition before changing it