I had seen that the Find/Replace window was far on the right side of my screen and looked a bit further.
It is displayed, but depending on the screen size, the position of the IDE on the screen and the width of the Tabs view the Find/Replace window position changes more or less to the right and may bee out of the screen.
Then whenever you try to display it again it will not see it again because it is still displayed but out of the screen.
This happens since B4A version 5.00.