Why i can't see the DrawDebugString in my Screenshot?

I have managed to take screenshots in-Game with this function:

The problem now is that the drawdebuglines are displayed, but not the drawdebugstring. Does anyone know how to solve the problem? I would be very grateful. Thanks in advance.

My C++ code for drawing the strings:

FVector TextOffset = FVector(0, 0, 20.0f);
FColor TextColor = FColor::Red;
DrawDebugString(World, HighestPoint + TextOffset, ObjectName, nullptr, TextColor, 0.0f, false);

The picture I got:

The picture I want (without the UI):