This problem is caused by using Booster software like Razer Cortex Booster that closes explorer.exe.
If explorer.exe is closed, X-Plane may behave in unknown ways. In this case, it will not provide the mouse events to REP, which, in turn, is unable to detect when the user clicks on the side menu bar.
Another cause of this issue could be using X-Plane on a secondary monitor. To solve the problem, make sure you’re running X-Plane on the monitor set as Main Monitor is Windows’ settings.
← Clicking the sidebar menu buttons do nothing