Why hints are not visible when a cursor is over them?

Why hints are not visible when a cursor is over them?

My question concerns visibility of hints in an application using
DevExpress (C#) controls. The application has a panel on which there are
several controls, and only one appears at a given moment. A user can
choose which control should appear by switching among them. The controls
have their bar with several buttons (different buttons for each type of
control).
The problem is that the hints on the buttons sometimes do not appear when
the mouse cursor is over them. They appear after opening the application,
but when the user switches to a control of the same type, the hints are
not visible. When the user switches to a control of another type, the
hints can appear, but not always (I could not find the rule). But always,
when the user goes to a window of another application and returns, the
hints appear. The property ShowScreenTipsInToolbars for the bar manager
has the value true during execution of the program.
Do you know the cause of this strange behavior? And what to do to make the
hints always visible when a mouse cursor is over the buttons? I am not the
author of the application (I was asked if it is possible to solve the
problem) and I cannot give too many technical details.