If you are using a compositing window manager, then try a stacking window manager.
If you are using a stacking window manager (more likely), which one? They are not all equal.
What is running, including any background processes?
The easier answer may be to the question:
What OS are you using. Assuming you are using the standard desktop environment and window manager of the OS then it would be easy to determine what the trouble may be, though only if we know which OS.
RPi = The best ARM based RISC OS computer around
More than 95% of posts made from RISC OS on RPi 1B/1B+ computers. Most of the rest from RISC OS on RPi 2B/3B/3B+ computers